What did I do on my first (work) day of retirement? My work friends and colleagues have previously asked me that question also. My answer: I did nothing at all!
My friends/colleagues said that I did nothing as an employee, therefore apparently nothing had changed. I reminded them that I did nothing better than anyone else; so my years of doing nothing served to ease my transition from employment to retirement
I use my cellphone as my alarm clock. The VERY FIRST thing I did as a retiree was to delete my workday morning alarm setting. What a liberating act that was!!
At first, retirement felt like a vacation. I felt that I would eventually have to return to work "soon". It took a few weeks of actual retirement before the realization of retirement started to take hold.