Recommend strategy for On-site scheduling

I have few on-sites lined up but I am having a hard time figuring out how to lay them out next month (hopefully in two weeks) The main problems are: - Coordinators take a while to figure out the actual date - The flights etc. confirmation takes a while - Travel fatigue - Interview fatigue This makes is very tough to start the scheduling for another company as previous one takes some time. Theres whole another issue about managing leaves. What is the recommendation from the community? 1. Add a buffer of 3-4 days in between these and not worry about the scheduling clashes (the process will take way longer and maybe have to deal with exploding offers) 2. Play the waiting game and then start scheduling another one Should I schedule Google's on-site first as they take most time for post-interview steps? #google #amazon #facebook #uber