I earn more than that and I post on MN relatively often - but I'm not prolific.
I do find the whole "higher earners wouldn't have time for Mumsnet" trope quite bizarre.
I've found that the more senior I am in a company, the more control I have over what I spent my time on and the less oversight there is. Certainly a five minute scroll isn't beyond the realms of possibility.
It also wasn't unusual for me to have a quick catch up while waiting to make a coffee, on my way to meetings etc etc.
Now I'm my own boss, so I work the hours that suit me. For instance I work much more effectively in the mornings, so it's not unusual for me to start at 6am, work through lunch and then knock off at 3pm (meetings permitting).
If the weather is nice sometimes I'll take the afternoon off and make it up on other days.
I do work incredibly hard, and when things are super busy sometimes I'll be working from 8am-10pm, but that's the exception not the rule.
Earning a relatively high amount definitely doesn't mean I can't sneak in a 10 minute scroll whether that's at lunch, in the evenings, or even in five mins between calls.