Does iPhone 5C require update before 3/11/2019?

10.3.3 is correct for the iPhone 5C. It is not affected by the November 3rd GPS issue, and will continue to work as it does now.

Update your iPhone or iPad software to avoid issues with location - Apple Support

No. That update is required for model 5 only (not 5c). Take a look here:--> Update your iPhone or iPad software to avoid issues with location - Apple Support

Regards

Giulio

The 5c will, yes. The iPhone 5 doesn't. 5c has an updated GPS reciever and does not require 10.3.4.