Expiry of Xbox GamePass Ultimate provided with All Access

Concerning the 24 months of XGPU that comes with All Access purchase of the XSX, is there a limited time in which I must apply it to my account? For example, if I currently have 36 months (cap) of XGPU, will I be able to apply the 24 months of XGPU that
comes with All Access in 24 months time (when I’m down to 12 months remaining) or will it expire before then?

:)