After checking in online with Singapore Airlines I received a boarding pass. This shows a departure time of 4:15pm but a boarding time of 3:15pm. Surely they are not going to board the flight an hour before departure.
So what's going on?
There are a number of times and cutoffs and activities that happen before a plane leaves. How long these activities take depends on how many people are involved, in other words on the size of the plane. These include:
How long to allow for all these will depend on how many people are on the flight, how many seat change requests you're likely to get, how much online checkin there is, whether it's an international flight, even how orderly people are when lining up and how smoothly they manage to get on the plane and get their stuff put away. Also, if the airport is extremely busy, the airline cannot risk losing their "slot" by loitering around at the gate, so they will plan things with a bit of buffer - closing the doors 10, 15, even 20 minutes before departure, and closing the flight 45 minutes or more before departure. It is not possible for you to argue with this buffer or board at your own schedule in this case.
Many international flights ask you to be at the gate an hour in advance, and label it boarding time, so they can have 30 minutes of everyone-at-the-gate-but-not-boarding to do their other tasks. Small domestic flights at little airports where nobody is coming in on a connection might ask for as little as 30 or even 20 minutes.
Now what does this mean for you? If you haven't requested an upgrade, don't need a seat change, provided your passport info at checkin, and have priority boarding, you can get to the gate just before the flight closes (no more checkins allowed) since boarding will usually have started by then for a large flight or is about to start for small ones. (I generally only feel comfortable doing this when I've taken that flight from that airport on that airline before, and know what the variable are.) If you are going to need to interact with the gate staff before you get on the plane, don't try to plan for it during the time that 300 people are lining up and shuffling on to the plane. Not only will it be unhappy for you and for them, you probably won't get the seat you want.
I just checked my previous tickets from Singapore Airlines and it seems to be normal that the boarding time starts 1 hour before the flight for flights departing from Changi Airport.
One reason for that is probably that the baggage checks at that airport are at the gate only and thus they might want to allow for enough time in case somebody's baggage needs to be checked. Even if you do arrive 1 hour early, you'll probably not be allowed to board so early, but will have to wait for at least another half an hour.
However it also states on my ticket that the gates close 10 minutes prior to departure, so if you don't mind not boarding later than other people, you should be safe arriving later than 1 hour before departure.
On a side note, I've had one or two flights from Singapore where the pilot would announce that everybody has boarded on time and that will thus be able to departure a couple minutes earlier.
Airlines ask people to come earlier on some flights for several reasons, for example:
So I am sure there are other reasons like that, some which make sense and others which make less. Whatever was the specific reason for your flight, might be hard to say. I never had to board in SG 1 hour before.
Singapore Airlines actually close boarding just ten minutes before departure, so there is indeed absolutely no need to get to the gate an hour before departure. Back in the days when I flew out of Changi pretty much weekly, it was standard procedure for me to arrive at the airport 30 min before departure. (Already checked in, access to citizen/PR lanes in Immigration, and I knew the airport like the back of my hand. Don't try this at home!)
As for why, they're just trying to get people to the gate early, and Changi's been ratcheting up the propaganda for a while now. (Pet peeve: announcing "Final Call" something like 40 minutes before departure, and switching to "Gate Closing" when it's actually getting close about 20 minutes before.)
That said, unlike most airports Changi T1 and T2 only do the security inspection at the gate itself, so it does make sense to show up a wee bit earlier than usual. And since SQ is a big operator of the A380 superjumbos, it does take some time to get everybody on board, and if inexperienced first-time travelers fall for it and queue up nice and early, it's a smoother ride for everybody else.
While sometimes the airlines are simply trying to get you to board early to speed up there turnround time, and don't close boarding until much later, there are some important occasions when this early boarding time is significant and important.
The most usual reason is when the flight will be boarding by stairs in the field and not by a normal gate. In this case the flight will take significantly longer to board than normal, because passengers need to be bussed to the plane. Be warned that boarding will close significantly earlier than normal in this circumstances.
I've had this happen to me several times, usually at Heathrow. Occasionally I've been caught out and had to scramble to get to the gate on time. You should be able to check if this applies to you if you look for your gate number on an airport map. Your ticket may also state the time at which boarding closes. Make sure you arrive well before that, even if it seems unreasonably early.
The airlines track the number of on time departures (and arrivals). It is a key metric both within management and to some of the public picking an airline.
One way to increase the chances of an on time departure is to get everyone to the gate earlier than really needed.
Arriving on time is closely related to departing on time because at busy airports once a plane misses its departure slot it may have to wait an hour or more for the next free slot.
A related trend is that the arrival times are padded so that if the flight gets a good tailwind it arrives early. This seems to make passengers happy even though the published arrival time is not the true estimated arrival time.
It is all a bit of a game to make flight appear to be on time more often...
Unlike other airports, the security checks are at the boarding gate. This cause boarding time to be must longer for singapore airports