There is no best time of day really so the time you go is up to you; some people like to book around 45 mins before sunset and get to see the city in daylight, as the sun sets and after dark.
In the morning you may get fog, then again you may not and in the afternoons you may get haze, then again you may not so pick a time and hopefully the sky will be clear - in's'allah !
If I was doing it I'd go for around midday but that's personal preference.
As for the hotel then if your flight lands at 7am it will be more likely 8.30- 9am when you get to your hotel as it is around 20-25 mins from the airport by taxi.
If they have a room free they will probably let you have it but you can't expect it as check out for other guests will be midday. Treat it as a bonus if you get the room earlier than normal time and they will let you use all of their facilities if you don't so they will store your luggage and you can have breakfast, go for a swim in their pool and a snooze on a sunbed - for this reason it's a good idea to pack swim things and suntan lotion at the top of your luggage then you can use their facilities to change.