Hi,
Picking a dateDepends on when you are READY!
I advice people to keep giving 1/2 mock tests per week and once the score becomes consistent (and of course is near to your expected score) then go ahead and take a date of after 3-4weeks.
Picking the time-slotDepends on when exactly are you fresh!
Some people are fresh in daytime and some in morning.
Personal preference is morning as I am at my best in that time-slot.
You can probably try giving mock tests in different time-slots and check your performance and then take a call.
Good Luck!