Next year I'm planning to go to Scotland. I'm really interested in nature and so I think the Scottish Highlands are worth a visit. Besides all the marvellous old castles I would really like to visit some famous lakes. First of all I'm interested in Loch Ness. I also heard from various people that there is a monster living in this lake. So when is the best time (season and time of day) to see it?
Right, despite missing out on the first day of my tour there while my train broke down, the rest of the gang went and unfortunately for me, I missed out on an opportunity to see Nessie. One day though, one day...
Firstly, you need to be aware of the geography. Loch Ness is in a natural cleft between Fort William and Inverness in the Scottish Highlands, and is 23 miles long. It's also nearly a mile wide in places, and is VERY deep (up to 226m). Statistically, this poses a problem for someone hoping to see Nessie, even if she does surface.
Next, consider the weather. Edinburgh, further south, has 186 days of rain a year. That's HALF the year. And it's considered the SUNNY side of Scotland. Wind, rain, mist and snow are a feature of the Scottish highlands (it rained every day but one of my tour, but it was still amazing), but don't help with visibility.
Next, the location north. Scotland is pretty far north. In winter, like now, by the end of November the sun has already set by 4pm. This doesn't give you much daylight time to go Nessie hunting. Statistically this means from June to August you're probably going to have the best shot, with weather and sunlight matching this. Of course this is when more tourists are there, and naturally this aligns with July and August being the most common months for sightings.
Most sightings have been early morning or early evening. This could be argued that it's because low light plays tricks on the eyes, especially with mist hanging around, but if she's reptilian or amphibian, they often try to avoid moving lots in the heat of the day anyway, so avoid searching around lunchtime.
There are boat tours on the water as well, so I'd consider that your best chance in summer, get out on the Loch and be close to Nessie. The castle in the north east also offers dramatic views and has had some sightings.
Good luck! We expect pictures ;)
Judging from this list of sightings, your best bet is in the month of August, but no later than October. May also seems pretty common as well. Most of the time the sun was not out when the reports were filed (a fairly easy thing to imagine, honestly).