Dynamically preventing Laravel from filling create_at field

I have a model corresponding to a table with "created_at" and "updated_at" fields. The default Laravel behavior is OK for my need:

• automatically filling "created_at" on inserts,
• automatically filling "updated_at" on updates.

Great, but for some reason (too long to detail here), I need in some cases to disable this feature (I mean dynamically disabling it during the code execution).

How can I do?
Thank you in advance

via Chebli Mohamed