Here's a link to Kodak's tech page for TMax & TMax RS developer. It has lots of information but nothing for Ilford film.
http://www.kodak.com/global/en/professional/support/techPubs/j86/j86.jhtml?id=0.1.16.14.30.14.7.16.14&lc=en
Here's the Ilford tech pdf for hp5+. It does show dev times with TMax at 20º C. but not at the standard 24º C.
http://www.ilford.com/html/us_english/pdf/HP5_Plus.pdf
Perhaps there is something you can put together between the two.
Until you work out your own EI and dev time for 24º, perhaps you can cool down your soup with ice and use the recommended starting time of 6-1/2 minutes at 20º.
Another note, you will find you have better results with at 1:9 dilution straight from the bottle than the 1:4. Longer dev time though. Also, no need to mix a stock solution. Just squeeze the air out of the bottle after every use. Make sure your working solution has enough chemistry for the amount of film being developed. I use 50cc of syrup for every 2 36 exp. 35 mm films or equivalent 4x5 (eight sheets). That makes 500cc of soup.
Peace! Sidney
