All cops have a grace period of 0.35s/0.45s, same as you.
In Overkill or below, it's 0.45s, in Mayhem or above, it's 0.35s.
Also note it uses the raw damage, so headshot will not be regarded as "a higher damage".
Put the decompressed folder into mod/, same as other mods.

Q: What's the grace period?
A: When you receive bullet damage from an enemy, a timer, which in Overkill or below is 0.45s and in Mayhem or above is 0.35s, will be activated. During this period, any other bullet damage less or equal to the previous plus 0.01 will be ignored. If you receive another shot that has greater damage, this damage will not be ignored; your AP or HP will be deducted, and the grace period timer will be reset.

Comments, suggestions and ideas for the thumbnail are welcomed.

Demo