yeah, that's really barely any time at all. I really enjoyed Inle Lake, but given your time issues I don't think it makes any sense. You also have an hour drive to and from the airport plus time on a boat to get to/from the lake.

I'd say spend the first day seeing some sights in Yangon (there aren't that many, but as noted the traffic can be pretty horrendous), then spend 2 or 3 days in Bagan before returning to Yangon for the last day.

There are a couple of day trips you can do from Bagan if you get templed out as pretty much the temples and monuments are what there is to do in Bagan. But it is stupendous.