Roundabout how long does the small generator take to come up, when only supply power to the servers?

A.
10 minutes or longer.

B.
5 to 10 seconds.

C.
5 minutes or longer.

D.
For the longest is about 15 minutes.

Explanation:
Small generators take from 5 to 10 seconds to come up, provided they are supplying power only to the servers.
References:
Charles J. Brooks, Server+ Certification Exam Cram 2 (Exam SK0-002), QUE Publishing, Indianapolis, 2006, pp. 227-240.