Espressif Systems ESP8266 Beginner's Manual page 9

From a microcontroller's perspective however, 3 seconds is a very long time (240 million clockcycles), so unless you do some
extremely heavy number crunching, or sending extremely long strings over Serial, you won't be affected by this. Just keep in mind
that you add the inside your
yield();
Sources
This is where I got most of my information to writ this article, there's some more details on the GitHub pages, if you're into some more
advanced stuff, like EEPROM or deep sleep etc.
https://github.com/esp8266/Arduino/issues/2942
https://github.com/esp8266/Arduino/pull/2533/files
https://github.com/esp8266/Arduino/blob/master/doc/libraries.md
https://github.com/esp8266/Arduino/blob/master/doc/reference.md
https://github.com/esp8266/Arduino/blob/master/doc/boards.md
or loops that could take longer than, say 100ms.
for while