Hours per week for my primary EC decreased by half during junior year; how should I report this?

Hi, everyone,

My time spent on my primary EC, playing a rare instrument, decreased by half during junior year, as I started learning a close (more popular) cousin of my instrument. I spent a lot of time freshman and sophomore year, perhaps around 20 hrs/week, playing that instrument, but now it has reduced down to 10 hrs/week, as I split my time between both instruments. I understand that all these hrs/week are just rough approximations (mine widely varies, as a matter of fact), so how many hrs/week should I list? If I list 10 hrs/week, then it looks as if I was doing nothing freshman and sophomore year. If I list 15 or 20 hrs/week, then it looks as if I am grossly exaggerating my time commitments as I have other activities now.

Thanks!