I agree with Charlie. There’s no significant difference in meaning between „up until“ and „until.“ I can’t even think of a sentence where the „up“in „up until“ could not be left out, or where leaving it out would cause a loss in clarity of meaning. The strongest writing style in English is style that leaves out unnecessary filler words, words that don’t add anything to the sentence. Many languages aren’t like that, and make free use of filler words that really can’t even be translated. Those filler words in other languages may add a nuance to the sentence that wouldn’t otherwise be there, but English doesn’t really work that way. An example of a meaningless filler word often heard in English is „like.“ For example, „It‘s like really hot today.“ Leaving out the „like“ here improves the sentence. Say „It’s really hot today“ and you’ve said the same thing, only with fewer words. Hence, you’ve made a better sentence. Using „up“ in „up until“ really adds nothing to the sentence either, so I’d recommend leaving it out. The „until“ is probably enough by itself.

There is no significant difference in meaning. You usually don't need to use the "up". It just gives a little bit more emphasis to what you are saying, for example when it's a 'big deal' that you achieve something by a deadline. - I was working on my assignment right up until the deadline for handing it in...