IIRC the DMS doesn't actually support 9.2, it requires 9.4 or newer I believe. (You should double check that, my information might be old)
So you would have to start by upgrading your standalone cluster to 9.4 or 9.5 (PostgreSQL itself has no problem going directly to 9.5), and then use DMS to move it to RDS.
Hmm.. interesting.. yep.. I've just seen that DMS requires Postgres 9.4 or above...
What about the time needed? Do you guys have any idea how long does it take?
I tried migrating a 300GB postgresql 9.4 cluster from Rackspace to RDS and it didn’t finish in 3 weeks, so we scrapped that plan and used Bucardo to migrate it which finished overnight.