If you want to make a split filter print, first you need to make a test print with the green (or the blue) filter in place. I generally set my timer for about 3 seconds when I make my test prints. Process the paper and find a time you like. This will show the best time for the highlight if you have used the green filter. Say the time you like best is 10 seconds. Put the second strip or piece of paper in the easel and while using the green filter set the timer for 10 seconds and then expose the strip or piece of paper. Now remove the green filter and place the other one in the slot and make another test strip on top of the green filter print. Process this and look for the black. Say this looks good at 8 seconds. Return to the enlarger and make an exposure with the green filter (10 seconds) in place and then swap filters and make the 8 second time with the blue filter. Process the paper. You now should have your first work print. What you need to remember is that the green filter controls the highlight and the blue controls the dark or the shadow areas. One thing that I see happen to first time split printer is the choices that they make might not be the best the right out of the box. Most tend to select a blue time that is too long and result in a dark contrasty photo. Consequently if you pick a time with too much green it will be a dull drab photo.
Yes, I use this method everytime I print. To the fact that I bought an Aristo VCL4500 cold light to simplify the procedure. It has two tubes in it. One green and One blue. I used the green and blue filters for several years before I got this head for the current enlarger.
This method is strikingly easy. You get right to the contrast and to the exposure time this way, and in my opinion, much more quickly than the more conventional way. It must be said, also, that there are people that will say that nothing that is printed with the above method can't be duplicated with using just one filter.(the traditional methods) Try it and see how you like it. I like the method and it makes a lot of sense to me. I have been doing this for several years now. Maybe going on 10 years now.