^ quickest you can do is new part every 2 days, because you changed from a league that raced everyday to 1 that race less often, design will take longer also depending on the current % of your car development will take longer as detailed in the rules
http://igpmanager.com/play/?url=rules [2.1]
+ what Jamie says since he replied before me..... easiest way would be to increase the amount of designers on each part [or only do 3 parts at a time, then 4 the next]