Walking is great - and entirely predictable. At a normal walking pace I would allow 10-12 minutes “all in” from CCR to a B Gate, and 15-20 minutes “all in” for a C Gate.

One tip - whilst it’s nice to get to the gate early for Group 1 boarding (if that’s your thing), there is really no need of you’re on an A380 in First from a C Gate - you have to “queue” through the automated boarding gates (not much) but the A380 has its own hetbridge for the First cabin so once you’re there you walk straight on and no queuing down the jetbridge whatever time you arrive at the gate - a nice touch