It takes roughly 3-4 days, if sent by govt boards, it takes even
longer, but its not the post office that's at fault in that case.

Registered mail going overseas takes longer, possibly up to 2 whole
weeks, they will tell you coz it needs to be registered.
When I was overseas and
recieved registerered mail, the post people were so sloppy, they
didn't make me sign for it, just chuck it in the mailbox, too
much!!! 
You can trace registered mail only locally, if its registered mail
in and out of singapore, sorry no such service, And I think you
have to pay a little premium to make it traceable.