For Viabtc, it only accepts submissions every hour, and being a user of it, the 100 submissions are all done within every first minute of every hour. If you can consistently push through a transaction on the first min of every hour, then sure, cheap out on fees.
Chipmixer looking to cheap out on fees and then use acclerators?
At least for now, it's the first second. Tried to get my transfer through for three days, every time putting the input exactly when the clock turns to full hour.