The 15-20 seconds is the built in reversal timer. On the Rovers, it was a dial that you could set from 0 to 90 seconds. The Aquaproducts web site has the T-jet listed as coming with a digital timer that you can set (again, between reversals) from 0 to 90 seconds. But, the actual product ships with a power supply that has a built in reversal timer that is not user controllable.
The 2 hour part is the overall run time, that isn't a problem. And, the t-jet did come with additional floatation, but that isn't the problem, it is reversal time. It reverses so quickly that it just stays in one very small area (so if I put it in the shallow end to start with, it would stay there for the whole 2 hours). It has no problem climbing the walls in the deep end.
I have spoken with Aquaproducts and they are willing to send me a different power supply, but are saying that I may have to change the plug end of the cord - not sure I want to do that on a brand new, $600 machine... Right now, it looks like the reversal is occurring every 5 to 8 seconds, which is way too short. I'll be on the phone with AP again tomorrow...