Changing date and time format in filename

I am trying to convert filenames in the format "Scan 30 Jan 2021 at 17.34.pdf" to "Scan 2021-01-30 17.34.pdf"
I can automatically extract the date into a custom date attribute but how do I do likewise for the time? I have tried to extract the time (nn.nn) into a custom text attribute to using the pattern 11.11 but it doesn't match. See screenshots at http://chrisbunch.uk/docs/S4.png and http://chrisbunch.uk/docs/S5.png.
Is this possible? It's a piece of cake with regex (apart from the month) but I gather regex is not available.
Chris
I can automatically extract the date into a custom date attribute but how do I do likewise for the time? I have tried to extract the time (nn.nn) into a custom text attribute to using the pattern 11.11 but it doesn't match. See screenshots at http://chrisbunch.uk/docs/S4.png and http://chrisbunch.uk/docs/S5.png.
Is this possible? It's a piece of cake with regex (apart from the month) but I gather regex is not available.
Chris