I agree. I think using the prepositon "on" referring to the end of a quarter is clumsy English. (Several decades ago I was a teacher of English for 10 years). "On" is more suitable when referring to a particular day. Even so, I think that the exact deadline is somewhat blurred by the use of "on" rather then "by".
I think the excuse from the company here is that Q2 ends when Q3 starts. I guess that could be 9.00 in the morning when the market opens on the first of July .