Because the standalone certificate is commonly used as a stepping stone to full ADIT certification, it is unlikely that an ADIT student will seek more than two standalone certificates (with the full ADIT qualification certificate being automatically awarded upon completion of the third ADIT module). However, once you have completed ADIT, should you wish to complete additional modules which are eligible for standalone certificates, this option will certainly be available to you!
Once you become eligible for a standalone certificate, you may apply for it at any time. The standalone certificate is not time-limited, although you will need to hold the required ADIT exam pass in order to apply for it, and each ADIT exam pass has a validity period of five years.