I think what you are suggesting is fine. I wouldn't break up a jelqing session or a stretching session, but doing one to completion and later doing the other to completion should be fine. You also might consider doing one longer jelqing or stretching session and then doing the other one the next day. In other words, do one one day and the other the next. I did/do a UJ session one day and my UV session the next. Never both on the same day. I put a lot of intensity into my workouts and this has helped me maximize my girth gains by both the intensity and the fact either my CCs or CS got a break each day. I quit trying for length a long time ago because that area just wasn't happening for me.