Hi, I've been on Novamix 30 for over 2.5yrs & I've always done the;
<inject> breakfast... lunch... <inject> dinner/tea... supper.
I've never deviated by skipping anything or having the meals to early /late just because I've just never wanted to botch things up unnecessarily. Obviously, these routine mealtimes can be far too inflexible for many people, so it may be worth thinking about the basal/bolus regime.
Point is, you can't just skip your tea, because obviously you need to inject, so you will need to eat something. You could maybe just have something light if you've had a big lunch, but do keep an eye on your BG levels after any "big (carby?) lunches" that you're not going to high afterwards, because even though you will need carb to sustain your levels until teatime, you still don't want to go overboard as you're not taking any insulin at that time. I normally test 2-3hrs after lunch to see if I need a mid-afternoon snack or not.