anywhere at JB CIQ can buy prepaid sim at 8am?
City Square and Komtar JBCC only open at 10am, so your bet will be those booths around. Not sure if they'll be open at 8am, though.
First up, few meters after customs clearance, just before the newstand is a Digi booth.
Down the escalator where people head for the JB Sentral bus station, there's a Hotlink booth.
A couple of dealers in JB Sentral itself, with Digi, Hotlink, and I think U Mobile from the 7-Eleven.
Out of JB Sentral towards City Square, there's a Hotlink booth behind the taxi stand, near the moneychanger.
The Caltex petrol station across the road from Komtar JBCC... have seen a banner for U Mobile... I think from the 7-Eleven there.
There seem to be quite a few dealers in the shophouses outside City Square too.
If you're actually driving in that early to head north, consider getting from the Digi dealers in Yong Peng like in Lucky Garden and Wing Ann rest-stops.