That’s what I do in IM prep but for winter training I find I’m not aero most of time as my race is far away.
As race time approaches my time in aero increases including doing FTP tests in aero, doing subthresholds with helmet on and neck strengthening exercises. I record how long is my longest time in aero position in outdoor rides and increase that from one ride to another. Once I reach 120min, I know that I’ll be fine for the full 180km.
However, intervals above thresholds and hard climbs are seated.