I think the point is that you should assume most engineers need large uninterrupted blocks most of the time most days. It’s not about a ratio of one to the other, it’s about needing 5-hour segments of time in which nobody asks you anything at all and you don’t have to say “sure I can help now” or “I’ll help you later” because you don’t need to say anything when you’re not interrupted.
Saying “I’ll help you later” usually comes with 5-15 minutes of lost productivity while you try to get your concentration back for what you were just doing.
Also, it’s often better to bundle questions together, usually at the end of the day, and document them like with an internal Q&A board, to reduce future needs to interrupt over that same question.
But, to put some number on this, I’d say later in the afternoon, if I’m not busy for a deadline, I’ll jump up and help on all questions.
Between 7 am and lunch, I will not help you unless it’s an absolute emergency. I simply can’t afford to if I am going to do my job. Between lunch and 4pm, say, it’s a crapshoot based on what I’m doing, but generally I would say I respond with “I’ll help you later” to 90% of interrupting questions.
Interestingly, on my year end reviews one of the most consistent pieces of positive feedback I’ve gotten across several different employers, is that I am extremely helpful and generous with explaining things, and that my explanations are usually exceptionally clear and offer insight that quickly clears up confusion and leaves impressive documentation behind for people to reference later.
It’s about communicating smart, not communicating constantly. I defer about 90% of the questions I’m asked, yet people look to me as “the guy who always answers everybody’s questions.”
The only reason would be actual urgency (not the pretend emergencies that businesses claim, either).