I'm not familiar with the Blink without delay approach.... It looks like I will be looking into it.
The problem is that I want a regular sensor reading (50ms or so), and to write that to a .csv file on an SD card. It seems this cannot be done in a strictly linear fashion as the SD writes can take a lot of time. So some reading pointed me towards the buffer idea, which got me looking into ISR's somehow.
The end goal is an altimeter for model rockets. I want to sample barometric pressure, and temperature at regular intervals and write them all to an SD card.