Look, there is NO "best time" or magic formula for deciding when to retire. That is not the way to do good financial planning.
Everybody's situation is unique. Are you a couple? Single? Children? Elderly parents? Any siblings? What's your genetic medical history? What are your future employment probabilities? What percentage of your income do you put away in untouchable savings? Have you opened a Roth? What do you pay in fees on your investments? How old is your car, and how do you plan to finance buying a new or less-used one? Do you own a home? How much will your property taxes rise in 20 yrs? What kind of maintenance costs will you average over the lifetime of this specific ownership? What kind of lifestyle modifications have you made to improve your health in the last five years?
What do you envision retirement to be? Does your partner/spouse agree? What if you need to make serious lifestyle changes (of any kind, physical, financial, social/mental) - how will that affect your plans? What if your partner dies before you reach retirement age? What if one of you becomes disabled, how does that affect your finances? Are you carrying sufficient insurance in whatever areas you are at high risk? Have you done your legal documents? Are they up to date? Accessible to all executors/trustees/agents/heirs? If one of you dies is the other prepared for the decisions that must be made? Have you set up access to your passwords if somebody needs to take over in an emergency? Do your heirs know who your tax advisor and attorney are, and their contact info?
Looking for an answer of "oh, if you've saved xx amt of $$, then you can retire at age xx" is dangerous. Maybe you'll be lucky and everything will work out. Maybe stress-testing your plans against not just one or two bad things happening, but three or four, or five bad things happening in quick succession - won't be necessary after all.
However, since my DH and I retired early, at the end of 2009 as the markets were collapsing and hysteria reigned supreme, I can honestly say in our case, proper planning made the difference. We had started financial planning in our late 40's (and yes, we're sorry we didn't start sooner, LOL). Despite having made less money than most of our friends, we were THE ONLY ones who were able to take a planned early retirement and start doing the things we wanted.
Five years later we have not had to make any adjustments at all in our lifestyle, despite rising costs of travel, an unexpected but needed major home remodeling project, and a huge increase in our LTC-i premiums.
So.....look at how you live. Decide how you want to live in retirement. What will that cost you? How will you best pay for it? Where do you have to adjust expectations vs expense? Then, start working the "worst case" scenarios - thoroughly.
Remember, you can't remove all risk from your life, but you can mitigate it to an acceptable level. Figure out where your biggest risks are, that might keep you from succeeding, and work on a plan to lessen those risks; e.g., increase your chances of success.
Yup, it's work. If you're a couple it requires a lot of discussion (sometimes we got so irritated at one another, we had to stop for ten minutes and take some deep breaths). And then there's more work, to get your lives properly organized (those pesky legal issues) and keep it updated. But it's necessary, and the process of handling how you die/become ill or disabled, is just as important as part of the whole retirement discussion, as is 'what age is best'?