It won't take long for transit. Basically, when you arrive you will be routed (perhaps via a long walk) to the transit security (I am assuming that you will have your onward boarding pass already), which is usually quick, then back into terminal 3.

I am not sure which lounge is pay-in access, but I probably wouldn't bother, either. There is a lot to see in DXB (if you're bored you could walk all the way to the end of Terminal 1 and back), and plenty of good food and drink options if that's what you're looking for.