The correct expression is "waste time."
For example; " I don't want to waste time learning expressions that are seldom (rarely) used."
"Lose time," is used in a different context.. for example if somebody goes out drinking and drinks so much that there are passages of the evening that they do not remember then they might say "I lost some time in the evening," (although it would be much more common to quantify the time lost - "I lost about three hours at the end of the evening," - meaning that the speaker does not remember the final three hours of the evening. Similarly, you could say "I had about three hours missing at the end of the night," to mean the same thing.