FilmDevMate
Warmer develops faster. Keep the stated time at 22°C and the negative comes out denser and more contrasty than intended. Two degrees is not a rounding error. It is a different recipe.
This is the single most common thing that goes wrong in a home darkroom, because temperature is the one variable that drifts on its own. You mix the chemistry, go and load the reel, and by the time you pour, the developer has been sitting in a room that is not 20°C.
Stand the bottle or the loaded tank in a water bath at the target temperature and wait, checking with a thermometer rather than by feel. For dilute one-shot developers, mixing with water that is already at temperature gets most of the way there. This is the only option that leaves you developing the recipe as written.
Many film and developer combinations have published times at more than one temperature. If the room is simply warm, finding a recipe at 22°C is more reliable than adjusting a 20°C one. This is what FilmDevMate shows: every recipe carries the temperature it was made for, so you can match the water you actually have.
Possible, but an estimate. How much development speeds up per degree depends on the developer and the film, and published compensation charts are specific to the combination they were made for. Shortening gets closer than ignoring the difference. It is not the same as developing at the stated temperature.
Only the development step is timed to a temperature, but the whole process should stay within a few degrees of itself. A sharp jump between solutions stresses the emulsion. In practice this means the stop, fixer and wash want to be near the developer, not that each needs to be measured precisely.
Development is the one step in film photography that cannot be undone. Exposure can be corrected in scanning or printing within limits; a negative developed too far cannot be made thinner. Spending two minutes on a water bath is cheap next to a roll that is not what you shot.
