Have not run into this in the past when voting from the client. Voted on one proposal then tried another and got this message using the Vote-Many command. Waited a good 15 minutes and still getting this message.
"......" : {"result" : "time between votes is too soon - 198c2be3e156c2a.......6a5f66acf4bba1 - 1537\n"
Version info:
Dash Core version v0.12.0.56-7154cdf (64-bit)
How long do you have to wait?
You should be able to vote on a proposal you haven't voted yet without any timeout. Check the hash/proposal again - probably you already voted.
To cast new vote on the same proposal you need to wait 1h iirc.
EDIT:
btw, have anyone noticed this recently?
https://chainz.cryptoid.info/dash/#!extractionDoesn't that mean ASICs caused decentralization in our case?

(temporarily anyway... I don't think this will last forever. The incentives are prone to cause centralization in the end, we're working on that problem as well)