Serve Time

It looks like something was lost in Mohan's question, since I don't read anything about a let serve.

If the question is "what's the maximum time between the end of a point and the execution of the next serve?", then I guess we're coming back to the principle of "continuous playing", i.e. there is no "< X seconds" rule, just the general principle that you should not waste time between points by shooting the ball to the back of the court, or doing an exceedingly long pre-point routine. But it's up to the umpire's appreciation.