A few tips from more than a decade with the CombiPlan:
If you start with the film in an empty tank, I would recommend a few minutes of pre-wash, as it "evens out" the beginning of the development phase (just add 20 seconds to the dev-time to compensate for the time it takes for the developer to replace the water in the emulsion).
Second, choose a developer/dilution which gives you medium to long development times (7-8 minutes or more), which helps in giving you even development.
These tanks and especially the holders are a bit fuzzy to work with. Make plenty of dry practice runs, first in light and then in the dark. See to that you have 6 blank or ruined sheets to practice with.
When done with the developing step, i.e. when you're about to pour in the stop bath, you can be pretty bold. There are two videos on youtube which shows how to develop with BTZS tubes. In the first video, when the development phase is done, Fred Picker (?) simply screws the cap of and puts the tube in a tray filled with stop bath. This is done in full white light. Once I saw the older version of the instructions, I tried it with my CombiPlan like this:
Develop like normal, but when there's 30 seconds left, I have only a red light on in the other end of the room. I then lift one corner of the lid and pour out the developer (in a jug or in the sink, depending on if I will reuse the developer or not). When the timer rings, I lift the corner a bit more and pour in the stop bath, after which I put the lid back and agitate for some 30 seconds. I then pour out the stop bath and pour in the fixer. The film is now definitely light-proof and I can take the lid off and agitate by lifting/dropping the film holder until done.
I know that this may sound controversial, but it's safe and saves you both time and effort.