I haven't tested it fully yet, but how do I change the blocktime to 5-10 seconds instead of the default 60 seconds? I'm testing this fork to see if it would work on my web app as the currently 60s on Ardor doesn't work due to the long wait time on block confirmations.
Most of the time you will find these kind of hard coded constants in the aptly named Constants java class. Usually you just modify the value and you are good to go. Sometimes there are other implications. Any serious project would require a good understanding of the code base.
About your specific question keep in mind that the block time is not something you can test with a couple of nodes. It's a fundamental parameter that affects the whole network and you won't be able to know in advance if it can be sustainable or you will end up with forking problems preventing the whole network to reach a stable consensus.