Sentence:  These cells were thawed at 37 ` C for 30 <WSD>min</WSD> and were deglycerolized by alternately centrifuging and mixing with descending concentrations of glycerol solutions ( 20 , 18 , 10 , 8 , 4 and 2 % ) . 
Meaning of the word marked with <WSD> tags:  a unit of time equal to 60 seconds or 1/60th of an hour