Getting a tertiary education can never be a bad thing. If you are motivated and want to be a pilot then I'm sure you'll make up the time gap once you finish and lets face it, you'll only be 21 when you do. You see plenty of 20-21 year old wannabe's stacking shelves in supermarkets while trying to get that elusive first job so I believe you can make up for lost time relatively easily.
Then when the time comes for you and supermarket boy to go for the airlines surely you will have an edge because of that pretty piece of paper you have. Who knows, it may just make the little bit of difference you need to get the job!!?? You'd regret not doing it then if you were the other guy.
I did my degree for the above reason and although I'm not there yet I think I'm in the same phase of my career of most of the other pilots my age in the area.
Hope all goes well for you,
Ref.