The recommended time for new Delta 400 shot at 200 is 6 minutes in Rodinal 1+25, or 11.5 minutes in 1+50. Both times are for 68°F(20°C).(posted 8543 days ago)As with all ILFORD recommended times, these are to be considered starting points for your testing. However, in your situation, I think you will be okay. This should yield a Gbar of about 0.50.
BTW, the new version of Delta 400 is faster than the old version, by about 1/3 stop or slightly more.
Regards, David Carper ILFORD Technical Service