Preparing a tincture would require 2-6 weeks of time. Once prepared, it is in a form ready to use. Remembering whether to apply it to the surface of the skin or serve it in a drink would require the apply prepared herb skill.
Okay, you're just disagreeing with me again. I see one interesting problem with what you're saying. That is, I haven't yet seen an herb in the Rolemaster game that can be prepared in more than one way. They all say either 1. brew, 2. ingest, or 3. apply. Certainly my knowledge isn't exhaustive. Are multi-preparation tinctures found in some product?
Look at the RMSS/RMFRP herb chart. Under Form and Preparation it says:
Brew - Effective when drunk 20 rounds after water is boiled
Ingest - Immediately usable and may be eaten, chewed, drunk, or inhaled, whichever is appropriate
Apply - requires 1-10 rounds to prepare; herb is applied directly onto injured area
Now, you could definitely say that 'brewing' and 'ingesting' require some knowledge. 'Brewing' requires that you leave the herb in boiling water for 2 minutes and then that the patient drink the brew. 'Ingesting' requires that the patient understand which kind of ingestion is appropriate, whether eating, chewing, drinking, or inhaling.
That said, it is very hard to understand why it is necessary to get a result of 111 in order to know you have to brew your tea for 2 minutes and then drink it, or in order to know you have to eat your loaf of herbal bread.
The only way this works in play is if 1. the character is already an herbalist-type or 2. the GM gives massive circumstance bonuses and ignores any results that aren't successes. I suspect a lot of GMs do just that.
On the other hand, 'apply'-type herbs are less straightforward and seem like they would need more specialized knowledge to use. How many rounds of prep exactly? What is the physical process of application: bandaging, rubbing, or something else? It seems like needing a skill would make sense. And the skill does say 'apply' and not 'brew' or 'ingest' after all.
If you require this skill for brew and ingest herbs in your game (and probably most people don't even bother), most players will quickly stop using herbal remedies rather than lose the dose (and equivalent money) when they fail to get a 111 result. One possible way around it is to use the
Use Prepared Herbs check of the prescribing herbalist or doctor instead of the character's. You could say that the herbalist is really the one doing the using and the patient is just following the instructions.