I am in the process of sending the response to reviews to a journal. It looks like it will take some days for the revision. In the reviews, the associate editor had commented the following
Finally, I would appreciate if you could submit your revised paper by Jan 12, 2018. If you cannot meet this deadline please contact us (firstname.lastname@example.org) to request an extension, otherwise your paper may be withdrawn.
I was wondering if it was OK to write to them asking for an extension or should I somehow submit the revision by Jan 12?