You are making good progress - keep it up!
But ...yes, you are still way off a 5 hour century ...
I've done a few 6 hour centuries, each having about 3,200 ft of ascent. It took quite a lot of effort to get down from 7 hours to 6, and it would take even more to get down from 6 hours to 5.
Don't obsess about your speed. Just keep riding and put in plenty of hard efforts, but also make sure you have easy or recovery days between them. I have a favourite hilly 25 mile loop and I used to go out once a week and try and beat my time on that. That kind of thing is a good way of motivating yourself to get faster, and of monitoring your progress.