If you contact the 3rd party insurance direct, it may take
longer because it's in their interest to sit on it, which can be
justified even better when the biker don't report.
Some Insurance companies give face only to workshop because they
have lawyers working for them. So no point risking legal fees over
delaying small few hundred dollar repairs.
In my case, the biker took weeks to make a report. But that's ok,
coz the workshop only took 1 - 2 days to make the small repairs. I
just collect the car with no upfront payment and let the workshop
take all the time they want handle all the 3rd party claims. Took a
few months in the end.
Maybe your scheme different from mine, coz I dun have worry where
to find parts when claiming 3rd party; the workshop will settle all
necessary to make a proper repair and charge all costs to the other
guy. But again, I didn't have to deal with IDAC.
Good luck! 
