Mash and boil times

[bargoon]

I see recipes that have mash times from 60-90 min and also boil times anywhere from 60-90 min. I understand some times the boil time is longer to get to a higher sugar to wort ratio through boil-off.

So if you're designing a recipe is there criteria for determining a long or short mash and/or boil time.

Thanks all

[Oginme]

Personal preference mostly.  I will mash a high gravity beer longer at times to try to maximize extraction.  Likewise, I generally boil for 90 minutes but will cut that down to 60 or 40 for low gravity recipes.  There is no set rule.