It takes about a minute for a blood cell to complete one round trip around the body, and in the episode about circulation seems to imply the entire process took all day. So it can be deduced that 1min our time = 1 day cell time. There are 11520 minutes in 8 days, so that means the Platelets can live to be 30 in cell years.

Please do not tag memes the image does not display or reference. (In this case, you tagged "this is so sad" and "alexa play despacito"; the image references neither. This makes documentation and sorting on the site more obtuse.)