Not sure the precise expiry, but yes, pay again to extend

For the 2nd question, yes, you can straight away register and use the number

Penang Usually takes a 3-4 weeks to get through a series

But not always

General idea is that bidding for next series is open sometimes before the current running is finished

Though not always the case where numbers goes fast like in kl or penang
Where ebid open might be 2 or 3 series down the line

There is no hard rules when a bidding starts
It will be open when it's opened
When bidding concludes after 1 week, and payment is made
Then you can register that number to the car and use it before the previous series is done and new series yet to be open