Just when a pitch raise or lowering is necessary depends on how accurate the final tuning must be, and the size and quality of the piano. Realistically, a pitch difference of a few percent can be accommodated successfully during tuning.
For average situations, when a piano's pitch is noticeably different from that of other standard pitched instruments, a pitch correction procedure is necessary before tuning. Whenever exact pitch level is critical, such as in concert or recording instruments, any pitch deviation must be corrected before tuning.
How long does it take to perform a pitch raise?
Everything being standard, a normal pitch raise is tuning your piano twice. So, if it takes 45 minutes to tune your piano, a pitch raise will take twice as long as that.
Extreme pitch changes on the other hand may require two separate visits to do pitch adjustments, else you risk breaking the strings!
In general, the longer a piano has gone without regular service, the more tunings is necessary to reestablish tuning stability. Like your car, your piano is a major investment which deserves regular servicing to keep it working well and preserve its value.