My point assumed that the Pay Bill project was already in your GTD system, so processed, clarified and written on your NA lists- In this case Fetch Bill.
Once you complete this NA it would take longer to add the NA (Pay bill) to your lists than just do it (okay that’s possibly arguable, but it’s not massively different) so just get on and do it.
I have a project on my list to Photograph the flowers outside the pub next door for a brewery competition. My NA is to sort out the equipment to take.
It’s likely that i will then go and photograph them, come back, download the photos, edit and process them, and then supply them to the pub, all in one go. None of these actions will be written down, as I will just do them.
However if the phone goes whilst I am downloading them, and I have to go and do something else, then the NA that goes on my list is “edit photos” (once started the download is automatic so nothing else for me to do).
My point about the 2 minute rule is that if the action AFTER the Next Action takes less than 2 minutes then just do it, don’t bother processing it, unless you get interrupted and can’t complete it.
Although it’s called a rule, it can be used in more than one place IMO.
This is a bit off the topic of the OP but...
I may have misinterpreted your point here, but just to make sure the 2 minute rule is clear for anyone reading this...
My understanding is that the 2 minute rule applies specifically to time you're spending on the processing/clarifying phase of GTD workflow. Ie: taking inbox items and other miscellaneous inputs and decided whether they are actionable and if there is a project etc. If an item is actionable and the action would take less than 2 minutes then the general guidance from David and Co is to do it in the moment rather than spend time organising and tracking it in the system.