Every lab has a fixed-sized container that they use for sample collection, be it blood, urine, or semen. Plus, a quantity is also specified for different tests. If one is appearing for a drug test by urine. One is given a cup by the lab which is conducting the test. The size depends on the laboratory.
The standard minimum amount required for a specimen is 30ml. There is no hard rule if the urine collected in the container is more than that. A test for steroids requires 60ml. About 5-10 ml is required for the initial immunoassay screen and another 5-10ml is needed for any confirmation testing. The last 10–20ml is kept frozen at the lab for any possible retest. The urine sample must be stored at room temperature for drug test.
For a drug test, a morning sample is not a must. It can be collected anytime. To match the minimum requirement of 30ml it is necessary for one to stay hydrated and away from activities which make you sweat a lot.