I've been testing the legacy 110 and liking it a lot. I've been using it for my grainier films instead of Rodinal, 400 and 3200, so can't help with your specifics as I don't shoot those films.
That said, I'd say test yourself - you can find some baseline times on the massive dev chart.
My testing for 35mm film (I always do this since a roll of 35 gives me a lot of data that will translate - to some extent - to MF or sheet film):
Find a baseline suggested time - for HP5+, if it was, say, 7 mins. dilution B at box speed (can't recall specifics) -
I'd shoot a 4-shot bracket of a test still life with highlight detail (styrofoam packing chunk), a gray card, shadowy stuff (dark fabric with a print) and a constant light source. Meter for shadows, and expose at 200, 250, 320, and 400 -
Advance one frame, open the camera back in the dark, stick a tiny tab of blue tape on the current frame, close the back, advance one frame...
Do this three more times for 4 sets of 4 brackets;
In the dark, take the film out, cut at each tape tab (there will be a blank frame there so precision isn't needed), store 3 of these sets in film vials, develop one at my best-guess time (4 frames is enough to hold still in a reel);
Do two more of those strips at times that seem interesting or proper based on how the negs look... if my first time was 7 minutes, maybe I'd do a 5 and a 12? Sort of depends on how the 1st strips come out. I'm very into shadow detail, so that's what I look for, and check highlight density.
Sleeve the film and label which strip got what time/dilution. Do a contact sheet with filter #2 and inspect the images for an idea of dev. times for specific speeds.
Maybe use the last snip to fine tune. Usually enough film left for another bracket or two, I usually test pushing to say 800 and 1600 and see how the film pushes.
And finally, do a few prints at filter #2 and see which combo gives you the best prints, "best" being up to you, but generally ease of getting the blacks, highlights, tonal gradations, detail, whatever you're looking for, without a fight and split filters or anything like that. You're looking for the "best" iso for your style (vs. box speed) and the best time for that speed.
There's a million ways to skin this cat, but everyone will tell you a different time. It's good to just find your own, you can do it for one roll and a couple hours work. And you'll feel all scientific.