I actually feed both morning and afternoon. If you feed a large feeding in the late afternoon, it is possible that they won't finish it all before going to roost. This sort of invites the critters of the rodent variety. The next day, they'd also have to wait until late afternoon, should their feed be gone.
Understand, chickens have survived for centuries and they wouldn't suffer either way. But, since you're wondering and you asked, I offer the above. It is easier to figure their feed intake for the day and offer that in the morning, allowing them all day to finally clean it up.
Since I have to gather eggs anyhow, I"m out there a few times a day. You probably want to collect only in the late afternoon? Thus, the desire to also feed them at that time?