the problem is in your call of charged there you are passing the argument --ln-path ~/.lightning assuming that you run lightning in your home directory thus you have to set ln-path to /tmp/l1-regtest/.
Now you say that this also did not work. So before I give you a solution let me explain what is actually going on. charged talkes to lightningd via an rpc-...
Since you say you are changing your OS clock, I am assuming you are using Bitcoin Core's built in miner for regtest. This miner will try to not produce invalid blocks.
To avoid the time-too-old failure, it will take the maximum between the median time + 1, and the network adjusted time (which is basically OS time). So when you set the clock too far back, it ...
I downloaded the bitcoin core source code,
changed the regtest node address parameters to be like the mainnet in the file src/chainparams.cpp.
Then compiled it, run the node on regtest and it worked like magic!