A cigar that has come to you by post has been through more than the box implies. Someone else’s storage, a courier van, a sorting depot, perhaps a flight, then your front step on a day that may have been thirty degrees colder than the truck. The wrapper has been flexing the entire way. The filler has been gaining or losing moisture in fits. The binder has done its best to hold things together while the conditions around it changed by the hour.
Thirty days at sixty-five percent relative humidity, undisturbed, is the working default I would suggest in nearly every case. The rule of thumb that overlays it: rest at least twice the time the cigar spent in transit. A cigar that took ten days to reach you, including a customs hold, gets twenty days minimum on top of acclimatisation. A cigar that arrived in mild weather from a nearby retailer can sometimes be smoked in two weeks. A cigar that shipped through January cold gets forty-five days minimum, sixty if you can spare them.
If you want the longer argument, I have written it: see How to Rest a Cigar. The short answer for most readers is thirty days. The shorter answer for the impatient is “longer than you think.”