I want to develop my Ilford HP5 plus shot at 800 with a delution of 1:100.
After consulting the massiv dev chart I found the values for film shoot at 400 and 1600 what about 800.
In my experience with stand developing, anything after an hour is generally just wasting time.
You are developing to chemical exhaustion...once the developer is, in fact, exhausted...nothing is happening.
If the developer exhausts in 60 minutes, then spending another 30 in the soup does nothing. If you're worried about it, go for 90-120 and call it a day. Keep in mind that, with stand development, you do not modify the amount of development by modifying the time in the developer! Keep the same, long, time for all ISO's.
If your film comes out overdeveloped, then decrease the total volume of developer you use. If it's underdeveloped, then increase the volume of developer that you use.
It's recommended that you start by using 5mL of Rodinal at 1+100. I add 1mL for every stop that I'm pushing the film. But, generally, I'll overexpose film by 1/3 to 2/3 and use 5mL per roll at 1+100. Soup for an hour.
Again, the timing doesn't matter as long as exhaustion has been reached...The fact that massive dev chart uses differing times for any particular ISO leads me to believe that whoever put it together doesn't understand Stand Dev technique.
As with all "new to you" developing procedures you should do a test first.
Save the roll you already have shot, until you do some tests.
Shoot a roll of the same film at the same ASA, clip off 4 or 5 frames in the darkroom and develop at a time close to the middle of the times on either side of your ASA ( 400 - 1600 ) that are listed on the MDC. ( I.E. 4OO ASA for 80 min - 1600 ASA for 120 min, would be 100 min )
If that does not give you the density you are aiming for then clip off 4 or 5 frames again and dev for different times. Wash, rinse, repeat as needed.
The Massive dev chart is great but you may need to adjust based on your own experience, darkroom procedures, temps and preferences ETC.
From the MDC.
Ilford HP5+ Rodinal 1+100 1600 - 120
Ilford HP5+ Rodinal 1+100 400 - 80