Redeem Gamepass PC code during Gamepass Ultimate?

I currently have the XBox Gamepass Ultimate as a monthly subscription, if I redeem a code for a Gamepass PC for 3 months now, will my Ultimate be replaced immediately? Or does my Ultimate continue to run until the end after manual termination and automatically become the Gamepass PC?

So, for me it was the case that I only redeemed the Gamepass (only for PC) after the Ultimate Gamepass had expired, otherwise I would have had a month less, otherwise the Gamepass for PC would have been upgraded to the Ultimate. So it's best to wait until the Ultimate Pass expires and then redeem it.

The code will expire soon, I'll just do it as late as possible