It also depends on the temperature, the time of year, cigars in sun or in the shade, what you're storing the cigar(s) in, etc. AND where you live as Hugh mentioned.

I live in Connecticut. I do most of my smoking in the car. I keep a ziplock bag in the glove box with a few cigars. There have been times where the cigars have been in the bag for up to a month (even in the winter) and I've never ruined them.

Now if the cigars were NOT in a zip lock bag but out in the open, it's impossible to even take a guess answer at your question because we need to know:
Temperature
Humidity
In direct sunlight or not

But tell ya what, I've had cigars dry out in less than an hour on a hot summer day with low humidity when left in direct sunlight. Ruined to the point that when I cut it, the whole end cracked and split.