Well it looks like whatever BrainSlayer did, worked ; so I got to say thanks to him and kernel-panic69 (I got to say your[kernel-panic69] one of the most friendly/respectful/generous mods I have seen on random forums over the years).
because on my WRT54GS v1.1 router the 'remaining lease time' (on Status > WAN page) reset back to the full amount (give or take a little) at the half way point (give or take some minutes) of the lease basically when previously on the r41686 build the timer would count all the way down to all zero's (although internet still appeared to work and 'may' still continue to work on r41686. but I never tested it long enough to say for sure since I always ended my tests within a couple of days or so past the end of the lease. so about 7-9 days or so.).
so basically those looking for a build for these older Wireless G routers like the Linksys WRT54* series routers can probably start off with r43192 (from May 19th 2020)... https://download1.dd-wrt.com/dd-wrtv2/downloads/betas/2020/05-19-2020-r43192/ NOTE: I am using the r43190 (from May 18th 2020) test build and I would assume r43192 is safe, which is more of a proper public release, and should be pretty much the same as r43190. so use r43192. at the oldest... it seems r41686 is probably a good starting point but if you want the 'remaining lease time' fix (which might be purely a cosmetic fix since I never fully tested r41686 to see if the internet would eventually drop) you basically need to start off at r43192 (technically r43190).
but with all of that said... ill keep a eye on this over the next month or so to see if it continues to work like expected with the 'remaining lease time' being reset around the half way point of the initial lease time. if anything changes, or especially if any issues turn up, ill make another post here.
p.s. it would be nice if someone else with a router similar to what's in the topic could make a post to further confirm my experience. _________________ Linksys WRT54GS v1.1 /w dd-wrt.v24_mini_generic (r43190 May 18th 2020) @ 240Mhz ; new Panasonic capacitors Feb 11th 2020 | ASUS WL-520gU /w dd-wrt.v24_mini_generic (r43192 May 19th 2020) | Linksys WRT54GS v6 /w DD-WRT v24-12548_NEWD_micro | Belkin F5D7230-4 v1444 /w dd-wrt.v24_micro_generic (r41392 May 19th 2020) @ 240Mhz