It's no big deal and delays for the NCT are many depending on where you want the test carried out. You have a choice of many test centres and if you have an issue with the delay you may book for another test centre. Alternatively, you can ring the NCT call centre daily and if there is a vacant spot due to cancellation etc you'll get it.
These are unprecedented times due to Covid and delays like these must be expected. After booking in advance, I would keep details of the NCT application in my car just in case the Gardaí stopped me.