For a pressure test/leak test/hydrostatic test of pipes what should be the test pressure and for how much time?

Most piping is covered by codes such as the ANSI piping codes. The site below has some references to other codes.

In general pipe is tested to 1.5 times its design pressure. This is for hydrostatic tests. For pneumatic tests the ratio is usually only 1.1 times the design pressure. The last time I checked there is no time limit addressed in the code.

In practice, a minimum of one hour is a good standard but should be longer if necessary. Because of the need to check all components in a piping system, the inspector should set the test time so this can be done. If it takes longer than an hour then the time should be extended.

I know from personal experience, just looking at a pressure gage is not sufficient to assure a good test. I have seen many cases where the gage reading actually went up due to thermal expansion but there were visible leaks in the system.

Pneumatic tests are really not the best to use for several reasons. If there is a failure of a component, the release of energy can be very large and dangerous. Secondly,in actual operation,  the relief systems for piping will exceed the pneumatic test pressure if there is a malfunction during operation. This is due to the accumulation pressure on most relief valves. This means the system will be subjected to pressures in excess of the test pressure and components like gaskets and threaded connections can fail.