I'd bring 'em back before the thing doesn't light off at all... like when it's 20F outside. Delayed ignition can also be somewhat dangerous. After the delayed ignition, does the unit then light off hard, rumble or make any unusually loud noises?
One thing that should be noted, many burners have a "pre-purge" function, where the burner runs up for 15 seconds to build pump pressure and establish proper draft for smooth and clean light offs. No oil is pumped into the chamber during pre-purge. And pre-purge times are always consistent - so pre-purge doesn't appear to be the issue in your case.
Did the oil service company provide any tune-up specs? Things like stack, smoke, CO, efficiency, draft? Did you notice if they used testing instruments to adjust the burner? They should have. If they didn't bother calling them back, call a real pro.
Is this unit a power venter? In other words no chimney and the unit vents on the wall outside your home through PVC pipe? That second motor you described starting up sounds like a draft inducer, but I wanted to make sure it's not a power venter.
I'd correct the flow on the coil according to manufacturer spec. The piping change shouldn't be a big deal in terms of time, materials or cost. A pro could do it in 15-30 minutes.