dear germany there should be no problem if you visit to and fro on a B1. Is your L1 process in US or overseas? but if you are in B1 while in US and your case is approved you will have to file a change of status. If you are overseas if it is approved, you will have to get a L1 stamp in the nearest consulate. Produce your approval notice while applying. if you want your case to be processed within 15 days talk to your company to process a premium processing. Statistics reveal that premium processing have higher percentage of approval.