If it was healthy live rock, then it will retain a great amount of bacteria, but in 20 minutes out of the water you will have a lot of die-off, and I would expect you should have had an ammonia spike of some kind right away. The way to test the filtering capacity would be to buy some janitorial strength ammonia from Ace Hardware (don't buy anything else anywhere else in my opinion) and add a VERY small amount (this is super strong stuff), wait 1 hour to mix, test ammonia, wait 12 and 24 and test again to see if it's getting taken down, test Nitrite and Nitrate also (before dosing and after). The amount of ammonia you need is probably only a few drops for a 29. I used 2 Tablespoons while fishless cycling a 225 and that brought it up to about 4 or 5 ppm
, so you need probably 1/40th of that to get 1 ppm
ammonia in your tank. Do a test on some water in a bucket and figure out how much to add for what concentration you want to see and extrapolate it out.
Theoretically, if you take cured LR
and put it into a new setup quick enough, you could avoid a cycle, but with the 20 minutes I would be expecting something.