crab,
(ATC) ............. " G - ABCD please state your ETA" (Estimated time of arrival).
(G-ABCD) ... "5 minutes"
I thought the idea was to be clear and concise to avoid any ambiguity.
5 minutes is not a time of arrival. for example it could be mis understood as "minute 5".
When you get asked for your endurance, would you tell them how much fuel you have left, what the capacity of your fuel tank is, how long you can fly for or perhaps guess what information they are after and let them work it out.
ATC is a precise language and is there for a good reason.