How Cold is too Cold

I have a couple decent jobs going this time of the year. Up this morning and checked out it was -1F. I could finish one of my jobs in a 2 days given decent weather , say high 20s or warmer. I sat on it for an hour and decided by the time I got the dump started , the backhoe started etc that it probably wasn't worth it. Last Friday ground was frozen about 6" deep here , and it wasn't all that cold then. Just curious as to most people do in this type weather.

How Cold is too Cold