If I understand your question, devices by themselves do not have any schedules in SmartThings. You have to have some smart app or routine associated with it and then you do the schedule there.
You can just use a routine, or you can use “smart lighting” which is the official lighting smartapp. Or you can use something like rule machine, which is very popular.
But you have to use some smartapp/routine to manage a schedule. You can also associate the same light with many different smartapps or routines. This gives you a lot of flexibility And you can apply different schedules to the same light based on different conditions. For example, you might want the light schedule to be different if you have guests staying in the house, or on a particular day when a cleaning service comes, or if you yourself are home or away from home.
By controlling the schedules through a routine/smart app, instead of just storing one per device, you get much more flexibility without having to remember to change the schedule yourself each time. 
If you deleted the one you had, it’s no problem, you can just reinstall it or use a different one.