(I'm going to request the moderators send this to the Microsoft Help forum, given that this is not really a PC hardware question but a general OS-oriented question)
The interval of when to sleep is up to you -- it makes no difference.
Windows Vista onward tend to do all sorts of "maintenance" activities at different times; anti-malware scanning is usually done in real-time, and the same especially applies for viruses.
Disk defragmenting, Windows Defender definition updates, a Defender "quick scan" (which is purely precautionary), and some other tasks are scheduled to run at a specific time of day (I think 02:00 in the morning local time). Microsoft Security Essentials also has something similar.
If the PC is asleep at that time, these tasks won't get run.
The time at which these tasks run is configurable in each application, so you can change it to meet your needs. To my knowledge, however, none of these applications will automatically induce wake-up to run. There may be software or ways to configure the PC to automatically wake up at some time (say 01:55am) then later shut off (say 04:00am), giving those scheduled tasks a chance to run, but to my knowledge this isn't possible natively within any of those programs.--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.