New town administrator Andrew Bisignani officially begins his job on Wednesday, but he’s already been spending significant time at Town Hall since leaving his previous post as Saugus town manager Jan. 6. “I’ve been doing my due diligence, meeting with department heads’’ and other town officials, Bisignani said, adding that former town administrator Mark Cullinan “has been very helpful with the transition. I’ve spent a lot of time with him. The town is in good shape, and we’ll try to continue to provide good services, and if we see an area that we think can be improved upon, we will.’’ Bisignani will work a full-time schedule, with 20 hours paid and the rest volunteer.