No, we test airplanes at TDC for leak down. The timing is a set thing at what ever degree the engine operates at for testing.
All the A&P that tested my airpalne motor while I watch the leak down tests did it the way I describe,
Then he did it wrong IAW AC43.13 1B chapter 8.14 which clearly specifies the test will be performed on warm cylinders at TDC. The procedure is rather involved and has the pressure introduced to the cylinder in stages whereas the average mechanic just introduces 80 psi initially.
A conscientious mechanic will try to achieve the highest reading by moving the prop back and forth at TDC to help seat the rings against the lands, others will simply open the air valve and record the number.
The cylinder leak down test is often called "the A&P mechanic's continued employment test" wherein over 25% leak down is considered a fail.
When the Air Force ran recips they didn't rely solely on leak down tests, they would periodically perform dynamic tests. (You oughta see an 18-cylinder engine with compression gauges plugged into each cylinder...looks like Medusa on a bad hair day)
