Well, unless you're actually really happy with your current employment and income. In that case, why even bother looking for something "better"? At that point that's just greedy.
The best time to interview is precisely when you're happy with your job.
You have zero pressure, you can practice interviewing, network and you can make extravagant requirements. If it doesn't work out, no big deal, you like where you are. But if it does, your career can make quantum leaps.
A quantum leap is the smallest possible state change
Free time is limited. I'd like to spend it doing something more rewarding than job hunting.
Job hunting can be a life changing moment. Something that will, literally, affect the rest of your life. If only because salary increases compound over an entire lifetime of working.
In other words, a $10k increase in salary might not seem much but it will add up, and not only will raises compound as well but future jobs will start at a higher negotiation level as well.
Of course, spend your time wisely but I think it's really short sighted to think "I'm happy at my job, I am going to completely block out all the recruiters out there".
Obviously, everyone will be different but I get 2-3 emails from recruiters on LinkedIn per week. Managing them takes me about one minute per week.
Compared to the number of times where I ended up on a phone call or having lunch/coffee with a CTO, VP of Eng, architect or senior engineer, it's totally worth it to me.
My suggestion: don't cut out that option until it really becomes unmanageable. Chances are you'll find it's worth the occasional disturbance.