You have two options for when a package can be used
When it's purchased
If a package was purchased at 2:05pm, it can only be used for classes/sessions after 2:05pm
The start of the day
If you want a package to be usable for all classes/session in a day, change your org setting
Go to Tools > Settings
Scroll down to bottom and toggle the setting
Note: this only applies to packages / subscriptions purchased after you turn on the setting