Unexpected Calendar Items for Monday Hour One Calendaring

Hi, I have been practicing my Monday Hour One.
One of the items in there was to follow up with clients. In particular, one client for whom I had let the ball fall by not sending her a quote when she had asked me for one.
I apologized and asked her if she still wanted one. She said yes but she needs it short-term.
I realize I have not left any slack in my calendar for these types of Follow-ups.
What is the best way to manage that? I think reshuffling my agenda after the Monday Hour is not recommended right?

Thank you for your help!