By "one year commitment" do you mean 8 of your ECs were started 1 year ago, or 8 of your ECs only lasted a year? If you only just started the majority of your ECs within the past year, that would raise some eyebrows. If you had 3 ECs... say FR to SO year and another 3 from SO to JR, 2 from JR to SR (etc)... then that is okay.
In general, more than a year is better. But it really boils down to what you got from the experience, not necessarily how many years you put into it.