It's like you had a faucet with cross section of 2 square inches, and 15 seconds with that faucet wide open would fill a jug. That jug holds 30 squareinches-seconds of water.

You may then use that water over the course of a day. That's 30 sqin-sec per day. That is not 30 square inches for a whole day. It's second per day.

Or watt hour per week or whatever.

Yes, it can be described like 0.00034722 sqin/day, and that corresponds to no physical object and that would be largely useless.

Why not Joules or Liters? Because that's complicated for anything electrical.

Pretty sure GP understands that, their point being you can't just wave away 'per unit time' when talking about it relative to generation, it matters.