When developing black and white, there are often differences between the film manufacturer's dev times and the chemical manufacturer's times.
For example: for Ilford HP5 @ 20c in Rodinal 1+25 in a small tank.
The time according to Ilford is 6 minutes with 10 secs initial agitation and then 10 secs agitation each minute.
According to Rodinal, the time should be 10 minutes with continuous agitation for the first minute and then tilting every 30 seconds.
Whose instructions do we follow?