I’m trying to figure out how to juggle multiple sports after several years of run then cycling focus. It is hard!
I have really good bike fitness right now and am trying to add in running. In my case, adding a 30-60 min z1/z2 ride would not be much of an issue to still hit hard stuff later. I’d start by keeping it to 30 min z2 and see how it goes. Drop to z1 if you need to. Definitely want to fuel it all regardless. It will hit your fuel stores for sure.
Honestly, the hardest part is just the mental toll it takes on me to keep it all going and switch gears all the time. I just want to knock out a good workout and be done for the day. When I start wanting to add stuff like multiple workouts a day it gets to be stressful.
You didn’t ask for general advice, but 4 days a week swimming is a lot compared to the running and cycling. Especially the running. Of the 3, swimming has always had the highest overhead - there is a big time cost for me to get in 45-60 min swimming compared to the same amount cycling/running. Maybe it is a seasonal thing and you are trying to build bike / swim fitness. In that case I get it.