To be doing that distance after only 5 weeks is a major achievement.
To be doing that distance on a 24 is quite an achievement too.
You should expect to be tired, and your balance to start to fail a bit as you near the end of such a ride. Don’t expect too much of yourself.
On rough ground, the legs get it real bad; on smooth ground, the backside gets it worst.
You asked for tips. Hmmm…
First, I’d say don’t push yourself. If you ride until it hurts, then stop for a minimal rest, then ride until it hurts, you won’t enjoy it and you won’t cover as much distance in the day. Especially as you get tired, take more frequent breaks. On a recent epic on the Coker, I found myself stopping about every mile towards the end. When I did 20 miles on the 20 a while back, the last few miles were similarly punctuated!
Secondly, when you do stop, get some calories down you, and some fluid. It’s as important for the mind as the body. Take a book/comic/newspaper and read it for a few minutes, unless you have a companion to chat to. Breaks in the ride should be part of the day out, not just a break to get your breath back an to recover the feeling in your legs!
Thirdly, put variety in the route. You can cover distance on tarmac or smooth paths, but riding on something more challenging is good for the morale. Take an occasional diversion when the opportunity arises.
Which leads to fourthly: when morale is flagging, and legs are tired, set goals - I’ll ride to that next bend, big tree, top of the hill… just something to aim for so that you feel you’ve earned your rest.
I noticed you referred to supported rests, by which I guess you mean you leaned against a lamp post instead of gettting off the uni. Why? The rest is only doing you half as much good if you’re still on the uni seat.
And finally, practise! The more you ride, the more natural it becomes.
And finally finally, enjoy the riding for its own sake, and the distance will come naturally. Set out to do the distance for its own sake and you may just end up hating it.