The required dose is actually quite small to be effective. I think the capsules are somewhere around 100mg, and I recommend 1 capsule 3 times daily before meals.
"To the Editor: Even low doses of mastic gum — 1 mg per day for two weeks — can cure peptic ulcers very rapidly, but the mechanism responsible has not been clear. We have found that mastic is active against Helicobacter pylori, which could explain its therapeutic effect in patients with peptic ulcers."
How long an ulcer will take to heal will depend on the size, and the cause. If it is from H. pylori then it should not take long to heal. If it from another source such as using NSAIDs then the source of the problem must first be removed then the ulcer can heal.