Oh. I feel you underestimate how long people can take to decide what to bid in a closed auction. I don't think it would be faster. If everyone can quickly decide on their bid in the closed-auction format, then the open auction doesn't take any longer, because they just bid up to that level, and not any higher.
Anyway, if it's faster for your group, I don't see it would do any harm to play that way.
I'm thinking of adding a 1 minute sand timer as well