Issue 1:
no longer than 3 hours of the event ending.
This isn't grammatically correct, and should be modified. Here is one option:
no later than 3 hours after the event ends.
Issue 2:
Tickets must be submitted
should most likely be
Tickets will be collected
This change isn't about grammar, but about choosing idiomatic words to go with "events" and "tickets".
Issue 3:
Finally, even with these changes the whole sentence still doesn't make sense. You don't go to an event and submit (or collect) a ticket - three hours after the event has ended. It's grammatical but nonsensical like "I turned off the television, to watch the program."
Unless you don't mean "ticket", but perhaps "voucher for a free meal", or something else.
By the way, it is possible to use "of" (which appeared in your original sentence) when discussing a time period. However, it doesn't go with "no longer".
If you get to the hospital within 3 hours of the first symptoms of an ischemic stroke, you may get a type of medicine called a thrombolytic.