Hi Nikolaj,
Realistically, I think the only likely way to get there is to ask your web hosting company to increase the time limit from 50 seconds. 90 seconds or more is the usual baseline. Either that, or see if they can make a zip binary available to use (so that PHP's internal zip-handling doesn't need to be relied upon - PHP's internal one is much slower). I don't see how to get from a situation where manipulating a 120Mb zip file in 48 seconds runs out of time to an eventual 640Mb zip file. Failing that, you should look for a better-resourced web host... any backup plugin that creates zip archives is not going to be able to succeed in this environment. Sorry to not have something more encouraging to say!
David
