That is probably a good idea, you can always cancel the other service once things have settled here at DreamHost.
The time required to transfer a domain registration can vary quite a bit, in my experience it is mostly determined by the speed your previous registrar responds to the request.
One thing, it might pay to confirm that the contact email address for the domain is correct before initiating the transfer. Also, you will probably need the domain 'auth code' for the transfer, you should be able to obtain this from your previous registrar.
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