When mixing, What's the best way to automate 1 of 25 tracks?
There is one measure where only one track needs to be solo, then all other tracks. I'm trying to avoid adding auto volume to all tracks.

Slip edit the other tracks to where you want them to start.This is non destructive.You can pull them back again later. 
 
You can use CTRL/A to select all. Slip edit by grabbing the leading edge and dragging 1 measure, now drag the one track back. 
Or de select the one track and slip edit the rest. 

You can also create a new bus and assign the 24 tracks you want muted to it, then automate the volume of just that single bus.

"assign the 24 tracks you want mute"  Yes, that sounds great!

I should mention Slip edit is letting the drum cymbal play, I need everything to stop completely except for the one track.

Oh I see this was in the middle of a song. I though the beginning. 
Then the automated buss is the best way.