At this point of the process, it seems unlikely that the company would withdraw its offer. Your question seems to hint that your future employer would like you to start pretty quickly. Maybe in a week or two? I suspect that, given the situation (starting soon and the recruiter taking more than two business days to get back to you), not being satisfied with the offer would justify postponing the start date. However, if the start date you mentioned is sufficiently far away in the future, I would advise you to be more sympathetic to the recruiter and not necessarily ask to push it back.
Revising the offer by adding an end date looks pretty unprofessional, in my opinion. It should have been there in the first place if they wanted to put a time limit on the offer. At this point, alterations to the offer should be negotiated between the two parties, not hastily added by the recruiter alone. I wouldn't necessarily deem it a red flag but, if I were you, I would be suspicious about the professionalism of your future employer.
Another element that would be important to take into consideration is the importance of the changes you requested about the offer. Since you're talking about mistakes and fixes, it looks like they might be minor issues like typos. I wouldn't be too worried about them even if, once again, it seems unprofessional. If the issues are more severe, like an error about your compensation or your responsibilities, then I would take it more seriously and would make sure that the offer is completely satisfactory before accepting it.