Is there a way to only allow a login to happen only at a specific time?
See this manpage for time.conf
user1 ; * ; Wd0000-2400 | Wk1800-0800
would allow the user user1 evenings on weekdays (wk), and all days on weekends (wd), and deny them the rest of the time.
yours would be something like
* ; * ; Al0800-0900