How many can you do as follows:
Using the wall for balance, or free standing if you've got it like that.
Kick up into the position. Count to 10, trying for a ligitemate 10 seconds. Lower yourself, then return to the top. Repeat until you fail, or know failure is inevitable.
I performed 4 reps, then a 10 count and knew I would not get the 5th. And be prepaired for some tingly and bloodshot eyes.