That would be 48 hours straight of UVB..... that will seriously make your chameleon upset and stressed as it will mess up the sleeping patterns. Hard to sleep with a bright UVB in your face all hours of the day for two days straight.
As for going two days WITHOUT it..... that would probably be okay sure, if it only happens once in a blue moon. The sun is not always shining in the wild, as there are weeks where it is overcast for days and days. This can be comparable to you leaving the UVB off for a couple days. But it's not something you should make a habit of. The difference is, the sun rays in the wild are super super strong, better than any bulb you could ever purchase. The days the sun IS shining, it is enough to make up for any days where the sky was overcast. You can't get a human-made bulb with that sort of strength. So I mean it's doable, but I wouldn't recommend it because if you let it happen once, then it could happen again and again and again... and it might become habit. And that would not be good.
Going out and getting a $20 timer and putting all your lights on timers would fix all your issues and you wouldn't even have to worry about this....