1)
-add to the event a Conditional Branch
-go to tap 4 and do script
-than enter: $game_system.ates.time.hour > "time"
("time" is of course the time you want etc)
you can change the > in whatever you need
you get the idea I hope

so a conditional Branch for 8..12 would look like:
2) look for something in your menu script like:
# Make a string for displaying the timer
min = @total_sec / 60
sec = @total_sec % 60
text = sprintf("%02d:%02d", min, sec)
(This is Sprite_Timer if you don't use a custom menu)
and replace with:
# Make a string for displaying the timer
hour = $game_system.ates.time.hour
min = $game_system.ates.time.min
text = t.strftime("%02d:%02d", hour, min)
should do the trick
remember to have the ATES script on because else it will crash