Instances per hour questions

First, are you allowed one instance every 12 minutes (60/5), five per 60 minute period, or maybe even five per "clock hour" (5:00pm - 6:00pm)?

Second, sometimes I'll leave for repairs or to empty trash from inventory and then it won't let that same toon back into the same instance. Is this a bug or does anyone know a workaround?

Not complaining- just want to understand the mechanics.

Thanks in advance!
Don't let your meat loaf.

Five per hour, the timer starts the moment you enter the first instance.
As for not being able to re-enter an instance that you were in before, that's not working as intended, but has been that way for a very long time.

Everytime you enter the instance portal 1/5/h gets used up. Hence going in and out 5x times locks you for 1h even if you did not even kill a single mob.

Thank you for the replies