At the moment this looks like it inherits the default value (1 year) - and it is possible to change this - by releasing a new AMP version of the Snowplow tracker.
This doesn’t look particularly difficult (add cookieLifetime as a new variable to the template) so someone on the Snowplow team might be able to pick this up (@Colm maybe?) - I’m not sure if AMP allow PRs outside of the vendor.
Thanks @capchriscap for raising this.
We are happy to implement this change, as Mike said, the AMP tracker is different from the other trackers where we would be more than happy of receiving external PRs.
We’ll give a look next week. I’ll keep you in the loop!