How about this:
Rosas concludes that things aren't turning around and he needs to make a decision on whether and when to make a change. He ends up landing on Finch, whom he already knows, likes, has interviewed for this job and maybe even wanted to hire in the first place, as the top choice to replace Saunders. But at that point, Rosas doesn't know whether he can get Finch mid-season. Finch is under contract with Toronto, so Rosas needs to determine whether he will be allowed to talk to Finch and whether Finch will take the job. On Saturday, he reaches out to Toronto and gets permission to talk to Finch. They speak, presumably about the job, general contract expectations, etc. Don't know if Finch has an agent, but assuming that he does, the agent would be involved in this as well. By Sunday afternoon, Rosas confirms that Finch is available now. At that point, he decides to fire Saunders. If Finch wasn't available, Saunders might have survived, maybe to the All-Star break, maybe longer.