Hello @Roxie423 ,
If you have Analytics and forwarding data to AAM via Server-Side Forwarding then you can ignore the first concern mentioned below:
"Delay between when a visitor qualifies for the experience and when they are included in the AAM segment to be used for XT"
However, above will need a slight change in Target where you need to get the real-time segment sync enabled with the help of Target Support(customercare@adobe.com)
If you are publishing your AA segment to Experience Cloud then it will be a 24hours delay.
Regarding Time-To-Live, you can set this to never expire in AAM for the specific traits by changing the TTL value to 0. However, please note that if any device/user is not seen online in 120days time-frame then this device/user will be considered as inactive and remove from traits/segments in AAM.
I hope this helps, please let me know for any additional question.