I would fix the set=up of the hybrid and save the first few rides on the new bike for a dry day and I totally agree with Ianrauk ypu do not have to wait until April - 5/10 minutes cleaning is all the is required to maintain your new bike if you avoid the worst of the weather/
Knee pain is likely related to the height of the saddle (too hugh or low) or you are trying to push too high a gear on the TT or you have a medical condition with the knee. Changing the bike is not the best way fix your knee issue.
Enjoy the new bike which ever decision you take
Slowly coming to this conclusion myself. I have a winter bike which serves in bad weather, does me for night riding and would be what I'd use on a TT or rollers if I had them. It also serves as my learning curve bike, doing odd jobs when they need doing so as to help me learn on a bike that isn't as valuable as my carbon.
BUT, the last time I used my carbon pride and joy was in December. It was dry, virtually no surface water, no muddy backroads and the bike came back pretty much as clean as a whistle. Only difference between riding it in early December and the summer is some hard case tyres I put on to cope with any extra crunt on the roads and some of the places I ride, I might be better off with them all year round anyway!
I compare the above to 3 rides over the summer on the other hand, where I was absolutely pissed on - two sportives and another long ride back from the south-coast.
So, perhaps the real difference is crap weather vs good weather bike, not summer vs winter. Just another perspective.
I agree with the poster above about the hybrid, it's set up incorrectly for your body geometry.