Heavy bike focus on two bikes - thoughts?

my guess is that it will be little to no difference for you legs.

the only difference may be on your butt.  As the seating position is different and hits in different spots- you won't be breaking those sit bones in quite as much on the tri bike as on the roadie.

only you know how much of a problem your butt becomes on long rides.

Yep...   over thinking!

I switch back and forth all the time.   Tend to use the roadie for hillier rides and longer outings.  It's rare that I don't have them both on the road during any given week.

The only way I might think otherwise is if you have some sort of crazy geometry on your tri bike, but I doubt that's the case?

Time in the saddle....

Excellent. I'll leave the roadie on the trainer, grab whatever bike I can, and let her rip!

Now, if in the group rides on the weekend the group says something, then maybe I'll change it out, but if it won't matter, then excellent.

And for the record, there's no crazy geometries going on. Basic Specialized Allez roadie, and a Giant Trinity Alliance A1 for the tri.

Round here the roadies frown on tri bikes in group rides.  That may be a consideration?

If you're riding with other triathletes I'm sure you're fine.

Same. We have two different groups for the weekends. The tri's don't care one way or the other, but the roadies do!

I have the same situation...and for the same reasoning!  I like to keep one bike on the trainer so I can hop on when convenient.

I just finished building my roadie, so happy to ride that for now. But my bike coach said to ride the TT bike if I'm training for a tri (duh) because the legs will be stressed at different points due to the geometry/body position differences.  So food for thought...