The very first cold start happens when the very first request comes in after deployment.

After that request is processed, the instance stays alive for the time being to be reused for subsequent requests. But for how long?

The following chart shows the typical range of cold starts in Google Cloud Functions, broken down per language. The darker ranges are the most common 67% of durations, and lighter ranges include 95%.

Google Cloud Functions have a setting to define the memory size that gets allocated to a single instance of a function. The CPU resources are allocated proportionally to the memory. So, in theory, larger instances could start faster.