I'm not on a local network, but I did enable that setting just in case. Anyway, I've just gone back on to re-check that setting was enabled and it's miraculously now working... which is good, except I'm now rather suspicious of whether to trust the rate limiting functionality not to eat into my daytime data allowance!
I paid for the pro version to get access to the new scheduler to remove my clunky set of scripts using the api to start/stop and speed up/down across the day, but I'm not going to trust it for a while yet. To be honest it's symptomatic of my experience with bysync from the start - great when it works, but just too unpredictable, flaky and unreliable to use commercially in my day job...