nice. in summary
take control,
set 80 rpm, wait
set 90 rpm, wait
set 100 rpm, wait
set 110 rpm, wait
your choice using small increments does cause int to overflow on an UNO/NANO. On some processors int is larger than 32,767
the beauty of using the variation of blink-without-delay is that you have really one thing, with different timing.
also, it leaves you with the ability to listen and get readings.
if you wanted to add in there the 'report settings' or 'report conditions'
you could bring that out.
are you planning on putting this into an enclosure with a display ?
if you are limited to access, you can add some LED's or blink cycles
for each RPM setting, you could turn on an LED. to show what stage it is in.
if you are planning on a display, you could add a timer and show current setting or poll the stirrer and report the actual RPM