(I'm a Google SRE. My opinions are my own.)

That's not what our 20% time is for, and 20% is way too small a number for that purpose. "20% time" (the way we use the term) is for personal/career growth/scratching itches.

Time spent on building systems that make our service better is my primary job. Manual remediation ("toil") is something to be tracked as a dangerous antipattern that must not be allowed to take over.

Toil and oncall response should be less than 20% of my time, together. At least half my time should go into engineering projects. If the level of toil is in excess of 50% of team activity then I would expect only percussive intervention to get the team out of this situation.