My listing asks people to let me know plans for their stay and why they chose my place. Most don’t bother.
I always have a follow up message to request this information and if they haven’t completed a profile or have a silly photo I ask them to tell me a bit about themselves and have a clear photo.
Airbnb’s standard check in time is from 3 p.m. Most hosts have anything from that time. So a 3 p.m. check in time is reasonable - a morning check in is not.
Did you ask him any questions about himself/plans/why he chose your place on booking? If not you can always ask him now, particularly if it’s shared accommodation.
Personally I am always there to check my guests in as this makes me more comfortable - hence I have a check in time of from 6 p.m. as I too work.