When does a 'meticulous' schedule become a problem?

Hey fellow grips, I’m grappling with something that’s been on my mind. This whole 'reactive approach' to scheduling is always highlighted, especially on smaller, faster-paced shoots. I get that things change constantly, a DP might change their mind on a lighting setup, or an actor needs more time for blocking. We've certainly had to pivot on a dime when a C-stand decided to spontaneously combust, or an AMIRA lens mount acted up.

My question is, when does that meticulously planned pre-production schedule (the one where every 15-minute slot is accounted for, sometimes even down to lamp changes on an M18 or a Forza 720B) cross the line from being a guide to being an actual liability on set? I've seen it sometimes create more stress than it solves, especially when the first few hours already wreck the plan. What are your experiences?