if your custom clearance is smooth, the the next tracking update should be Customs clearance processing complete.
just wait for the update, another way to find out will be through pos malaysia website track and trace page to see the updates.

if your item is stuck at custom, you can go to clear it urself or appoint pos malaysia as ur agent to clear your item for a fee (rm49.50 if i'm not mistaken).

hmm... usually the custom clearance takes one day, max 2-3 days.
if like that, i suggest you calling them up to be sure if you don't want to wait for online tracking update.
next tracking upate from pos malaysia should be 'Departure from inward OE/Send item to domestic location' if there's no custom delay.

USPS express mail should reach within one week if there's no custom delay.