The rate of the pressure loss is only one question in the safety equation.
The real question you have to assess is whether or not the gas is pooling up to a dangerous gas/air ratio near a source of combustion. Just because you don't smell mercaptan does not mean the gas has dissipated.
Only your local ordinance can tell you what's acceptable but here is what Home Depot has to say:
Acceptable Gas Line Pressure Drop
In order to pass gas line pressure tests, lines must hold a specific psi for the length of time mandated by local codes. When testing for leaks, there will be some natural rises and drops in the pressure of the gas line.
It is common for standard gas line inspections to require lines hold three times their working pressure load for at least 30 minutes. Typically, if the gas line loses approximately 2 psi from a test of 20 psi on the line, the lines are acceptable. Conversely, if the line loses more than 10% of the pressure, it may have a leak. This can be true after a 30 minute or even a 24 hour test.
Environmental factors also affect gas line fluctuations. Heat will cause line pressures to rise while cold temperatures will create a drop in pressure. As days and seasons progress, these conditions correct. It is normal to see drops overnight, and they do not typically indicate leaks in the line.