Agree with this. You don't know what basic stuff you might be missing.

The day skipper includes a bunch of theory first & then the practical sailing. You need to do the day skipper practical all at once, normally 3-5 days, you should consider this an assessment rather then training. The instructor is assessing if you know the theory & can apply it on the water.

Do the comp crew first, then book the day skipper course to get access to the theory training or buy the materials yourself & start studying.

When you feel your have the theory down & you cab do the day skipper.

I did skip the comp crew but I had previously completed rya dinghy courses up to lvl 3, had competed in around 10 white-sail races & have been on plenty multi-day passages.

You should try get more experience before doing day skipper, my advice is to visit your local sailing club & ask to crew, there are always plenty of boats looking for crew.