Some species of mosquitoes do go away at night while some other species of mosquitoes become more active at night.
I've still been bitten by mosquitoes at night although in my area the mosquitoes are most active during the day but in most areas mosquitoes do tend to go away at night and come out during the day.
So it can depend on your area as some people get bitten the most by mosquitoes during early morning hours and some get bit more by mosquitoes during the evening or night hours.
I would recommend getting a mosquito magnet which uses propane and draws the mosquitoes in and although they cost quite a bit they're worth the money if you want to take your yard back during mosquito season.