There is generally no delay in making the credit line available for transactions. A credit card itself is a line of credit. However there may be instances where the card issues takes executive decision and blocks further transaction as a risk mitigation measure.
In case of payment of dues the credit line is updated as soon as the bank or the card issuer received the fund. This is all automatic process.
There are various ways one can upload the dues payment on the card.
Via Bank Transfer
Via Card To Card Payment