How long to migrate SBS 2003 to 2008?

How much time should I expect to spend migrating a SBS 2003 server running Exchange/AD/DNS to SBS 2008 on my first time with SBS? Not expecting exact time here, just a range like 2-4, 4-8 hours. Not sure how much time to allow in my plans.
The 2003 server has a dozen users with 20-GB of mail. Nothing outrageous. Both servers have a Xenon CPU, GB Ethernet, RAID 5 and are decently fast.

Justin S.Asked:
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Glen KnightCommented:
I would set aside probably a couple of days to a week, this is because I move mailboxes overnight.

You also need to allow time to backup data from the 2003 server and restore it to 2008 which if you don't want down time will also need to be done overnight.

Public folder replication.

Once you move the mailboxes you want to make sure that both exchange servers are up and running together for a couple of days so that all clients update themselves for the new exchange server
Justin S.Author Commented:
Thanks. I was looking to do this over a weekend as I can take the server off-line Saturday.  Other than mailbox and data moves, does a full day seem reasonable, or do you think I will need to go in on a Sunday too?

Glen KnightCommented:
A full day should be fine.
I normally do the actual installation in a few hours in the evening then migrate the data over the next couple of evenings.

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