Of all the responses, the swimming makes the most sense. Yes, weightlifting is benefical, but you have to be careful. I'm an old Cat I tracky and a Cat II roadie. I weightlifted. I had great power, but couldn't climb my way out of a paper bag ( I let myself get too big in the upper body). You need to look at what you want to do and design your off season training around that. The key is balance. Cyclists' have good strong backs but tend to be week in the abs. Ab work is essential. In fact an overall strong body core will help every aspect of your cycling. It doesn't need to be big, just solid. Swimming is by far the best bang for the buck when it comes to overall body work. If you choose weightlifting, be careful not to let yourself get trapped into the "I want to lift just 10 more pounds than I can now" mindset. It will mess you up for cycling. Trust me on this. For next springs time trials, get some type of load trainer (Wind, magnetic, fluid, etc) and get on it. Do a 30 - 60 minute workout in the biggest gear you can turn 90 rpms two or three times a week. Add swimming and a sit up/push up routine and come next spring you be tearing up the road.
Enjoy,
scurry