I agree that it depends on how you expect the employer to react and any other circumstances that might be a factor such as bonuses, etc.
In my own case, my employer was a relatively large company in a fairly specialized field. I reported directly to the CEO for North American operations. I knew I was not indispensible, no one ever is but I also knew they were not likely to find a replacement within 2 weeks either. So I waited till after my annual lunch with the boss and receiving my bonus cheque before telling him that I planned to retire in a year. He asked if I was kidding and I said I was quite serious.
At the end of that year when we had lunch and I got my bonus cheque, I told him I was ready to go and asked him how much notice he wanted me to give. I expected something like 3 months. Instead he said he hadn't taken me seriously and asked me for a year's notice from then. I said I'd have to consider what to do.
I did some math at home and went back and told him I would agree to 3 months notice or quit that day and agree to sign a consulting contract for one year. During that year, I would work an average of 3 days per week with the days to be of my choice but with no gap longer than 2 weeks. As my earning were commission based on sales, I would sign a contract equal to the amount of my last year's earnings plus bonus as well as all other costs paid by the company. ie. company car, all benefits they paid for etc. That basically totalled twice my last year's income. He went for the year of consulting. So you could say my initial retirement lasted 1 day, then I became self-employed for a year working an average of 3 days per week for the equivalent of 10 days pay. Worked for me.
On another note though one thing I would advise anyone to do is not burn their bridges behind them. It's always a good idea to leave with them wishing you well. A good example of that was one of my 2 sons who after about 15 years with one company in the financial sector, was head hunted and given an offer he couldn't refuse. He talked to me about it and my only advice was, to say he was prepared to give them whatever notice they wanted and was leaving not because he was unhappy with the company or the money but only because it was not only a great offer, he also felt it was time for a change. I also advised him that if they offered to match the offer he had been given, that he had to say no. Otherwise they would never know if he had held a gun to their head and that would cause resentment.
He worked the month's notice they asked for and then took the new job and within 3 months of doing so, discovered that what he had been told and what the position actually was, were not the same thing. He called his old boss and told him things were not working out and he was hoping to network with people he knew in the industry and move on. He got a call the next day from the VP of another department in his old company who offered him a position that was also a promotion from the job he had left. Gave the new employer 2 weeks notice and left. He wasn't worried about burning that bridge.
The point being, even an early retiree might discover they got it wrong and need to go back. So don't burn bridges if you don't have to.
