I made a hotel reservation through Expedia under my name for two people but my friend will arrive one day before me. The duration is 8-14. I'm arriving on the 9th, my friend is arriving on the 8th.
So can he check in?
Depending on the Hotel, this may or may not be a problem.
I have worked at many different hotels in the US, we need to see an ID with the same name that's on the reservation to check in the room. I have fudged this rule on occasion (for spouses, siblings or children who can produce an ID with the same last name).
It would be safer to call the hotel ahead of time and add another name to the reservation. Most PMSs support multiple names on a reservation, so you should be able to keep your name on it as well.
I am assuming you have booked one room under your name, but your friend will arrive first. This could be a problem. To prevent fraud, many hotels insist on seeing a credit card with a name matching the name on the reservation, especially when the reservation has been booked through a third-party booking site like Expedia.
I would contact the hotel in advance to ask about their procedures; ideally get a response in writing. In many cases, you can complete in advance a credit card authorization form provided by the hotel, to be carried by your friend, which the hotel will accept as proof.