It’s fine to switch it up.. You’re currently doing something like circadian fasting which mimics your body’s natural eating patterns. If you’re feeling good, should try for 17-18 hours on days you’re not having that early dinner. You most likely won’t lose a ton of weight long term unless pairing this circadian fast with a low carb/ketogenic diet though, but you will improve many of your key biomarkers. Most important thing when new is to force your body away from carbohydrates so your body has to learn to start using fat for fuel.