We recently had a mash that started fermenting slowly. the next day's cook actually finished at about the same time. How long can a finished mash sit waiting to be distilled? We can do two stripping runs in a day, but would rather not. will an extra day matter after the mash is finished?
In this part of the world (Tasmania) all the other distillers make a "Scotch " style and they take pride in being able to leave their wash for several days after fermentation has finished gassing. They claim it makes a better whisky.
I believe that the only concern that you might have with letting a mash sit for a while after fermentation would be bacterial contamination (which, as Pete correctly points out, is not necessarily a bad thing and contributes important flavors to Scotch-style whiskies).
If you, for whatever reason, are trying to minimize bacterial contamination of your mashes (I personally do), then I believe that you should be more concerned about the lag in the start of your fermentation than a few extra days after fermentation has completed. The lag indicates that your yeast had trouble getting started, which leaves TONS of room for lactic acid bacteria (as well as enterics and others) to flourish. This bacterial bloom can further inhibit your yeast.
Once fermentation is complete, the pH and ABV of your mash tend to inhibit the logarithmic growth of bacteria (though they'll still grow, for sure).
So my answer to your question is no, I don't believe that another day is going to be detrimental to your mash. You may want to keep an eye on that spirit, though, because if you did get some undesirable by-products from a bacterial fermentation, the damage could already done. In my own case, I notice a persistent haze in the early hearts (when proofed down to around 35% ABV) when the LAB gets out of control in my fermentations.