I use a selenium/sepia split tone on quite a few of my prints. FWIW my process is: dev,stop,fix (TF4) 10 min wash, bleach till highlights show the desired effect, 3 min wash, sepia tone 1 min, 5 min wash, selenium tone until shadows reach desired density or tonal shift, 5 min wash, 5 min Heico Perma-wash, 15 min wash.
The effect of the sepia toner is determined by the amount of time spent in the bleach so if you bleach too heavily, the sepia toner will "overtake" the image and leave nothing for the selenium to work on. Conversely, if you choose to do the selenium toning first, don't leave it in long enough for the highlights to become changed or the sepia bleach will have no effect. With the bleaching and selenium toning phases, length of time means little so use your eye as a judge. The sepia bleach acts extremely quick once it takes effect so you may want to dilute it quite a bit in order to give yourself some leeway. Also, I almost always make more than one straight print since I often find that the toning results aren't what I desire and I need to alter the time spent in one of the baths. Its a lot easier when you have multiple prints at your disposal to work with. Good luck. I think the sepia/selenium split provides stunning tonality and impact when you get what you are looking for. Its well worth the extra time and effort. You may very well find that the untoned versions pale in comparison.