Hi Manfred.
Take a look at the utime module: https://docs.micropython.org/en/latest/library/utime.html#module-utime
It contains many functions related with time that should have what you need. Unfortunately, at the moment, we don’t have any recipe for timestamp.
We have this datalogging project: https://randomnerdtutorials.com/low-power-weather-station-datalogger-using-esp8266-bme280-micropython/ but timestamp is not included in the code.
Then, let us know if you found something or if you need anything else.
Regards,
Sara