I am commuting to work so all of my rides will be 2 rides per day (since I have to go home).
The plan is to do my hard work in the morning and a steady ride in the evening.
would I do the steady ride home at my LTP? or keep it under?
Is one hour enough to get benefit? or do I need to find longer routes and do 90 minutes?
thank you!!
I’m only using derived data for my commutes unless I take the good bike (very rarely in this weather)
. But
I check what ATA is saying in between the two. If the ride in was hard enough to make me ‘tired’ then it will recommend endurance and an interval target around lower threshold. If it doesn’t think I’m tired then maybe I hit intervals if I also feel like doing that after a day of work.
terrain. Your mileage may vary but my commute is decidedly more downhill on the way in so it makes a bit more sense to cruise that than try and hit targets on the way
time wise I’d say an hour especially of intervals definitely has benefit (I’m on ~2 stars) and you’d be getting 2 hours not just 1. You’ll just be missing the very specific benefits your body gets from long continuous efforts but otherwise plenty of good time.
If you want to keep your easy rides easy, I generally recommend to use LTP as the upper limit for your endurance rides, rather than the target, if that makes sense. I’ll loosely keep an eye on HR and make sure that it’s around ~70% of HRmax, keeping in mind that my HR is often skewed by hydration (or lack thereof), weather, & caffeine.
As you’ll soon discover, many times my favorite answer in this forum is ‘it depends’. 
Ultimately the key to increasing fitness is the principle of Progressive Overload (e.g. in order to become more fit, you need to do more than what your body is used to). Rather than looking at the commute home on its own, I’d consider the cumulative load of morning + evening commute (in XSS) relative to your Training Load.
If morning XSS + evening ride XSS >> training load, then we would expect you to gain fitness. As your TL increases, you might find that these rides contribute to maintaining your fitness, but might not be enough to build additional fitness. At that point, you might consider adding on a few minutes one (or both) ways to continue building fitness. However, keep in mind that you can’t infinitely increase fitness, so at some point, you’ll need to cut back & expect TL (and fitness) to drop a bit. For many in North America (myself included), it often coincides with the decreased daylight hours brought on by fall