It ends up giving you about half of your vote value in curation rewards. As long as you vote after the five minute mark, it doesn't seem to make much difference. When they forked the Steem code, they changed it so that 1 VEST = 1 BLURT on the first block. Doing that affected how the formulas work. The reward curve was adjusted for the vote values, but it was left the same for the curation rewards, since it was almost linear by accident.
@rycharde would be able to explain the math behind it better than I can.
So the TL;DR is that as long as you vote after the first five minutes and before the last 12 hours of the payout window, you will get roughly half of your vote value regardless of who voted before or after you.
Thanks a lot for clearing this out! :)
For more information about the planned change to the reward curve in the next validated hardfork of the Blurt blockchain (release date not yet defined), you can refer to the post Blurt HF09 Candidates | Community Vote for more details.
Currently, Blurt's voting system is more similar to Steem's than Hive's. It is more beneficial to vote after the 5-minute mark but before the big upvote, as well as to upvote within the first 24 hours (the notable difference depends on the value of your upvote, with a curation account like BeBlurt, the impact of the time of upvote can be seen clearly based on how old a post is.).