Taking a pill of 60 mg of mestinon gave results in 1/2 hour that lasted for about 3 hours. Sometimes I took 90 mg. It is not a drug that takes days to work, it works like aspirin, fast. I took it about every 3 hours during the day when I was at my worst.
Some folks are started at too small of a dose to have an effect. I think at least 60 mg is needed, and my doctor had me try 120 but that was more than I could handle -- the side effects were too strong.
Mestinon can give you digestive problems (very uncomfortable cramps, and diarrhea) so I took mine with some food (a snack bar) and took loperimide (Imodium) with my morning dose to make the digestive problems less. It also made me twitchy, some night leg cramps, profuse perspiration if I was working, but it was made my functionality so much greater than without, I took it anyway. And I did get adjusted so the side effects were less.
As it only works on the symptoms, not the cause, most of us have to start a course of immune system suppressants too. A few folks get by on only mestinon.

Good Luck Russ

I was started on 60mg 3x day. Yesterday was my first day and breathing seems to be my major issue at the present. It did did seem to help lessen my struggle But did not make me feel

Some folks with MG seem to have no or little response from Mestinon. I think most of us see quite an improvement with it.
from www.myasthenia.org

Cholinesterase Inhibitors (mestinon is one of these).

ChE inhibitors retard the enzymatic hydrolysis of ACh at cholinergic synapses, so that ACh accumulates at the neuromuscular junction and its effect is prolonged. ChE inhibitors cause considerable improvement in some patients and little to none in others. Strength rarely returns to normal. Pyridostigmine bromide (Mestinon) and neostigmine bromide (Prostigmin) are the most commonly used ChE inhibitors. No fixed dosage schedule suits all patients. The need for ACh inhibitors varies from day-to-day and during the same day in response to infection, menstruation, emotional stress, and hot weather. Different muscles respond differently; with any dose, certain muscles get stronger, others do not change, and still others become weaker. Adverse effects of ChE inhibitors may result from ACh accumulation at muscarinic receptors on smooth muscle and autonomic glands and at nicotinic receptors of skeletal muscle. Central nervous system side effects are rarely seen with the doses used to treat myasthenia gravis. Gastrointestinal complaints are common; queasiness, loose stools, nausea, vomiting, abdominal cramps, and diarrhea. Increased bronchial and oral secretions are a serious problem in patients with swallowing or respiratory insufficiency. Symptoms of muscarinic overdosage may indicate that nicotinic overdosage (weakness) is also occurring. Excessive nicotinic receptor overdosage results in Myasthenic Crisis characterized by severe generalized weakness and respiratory failure.

I have ocular MG. I started taking Mestonin a week ago Tuesday. I'm only taking 30 mg to start because I had severe GO issues the first 3 days. My eyelid is a little less droopy during the day. I have less intense twitching in my face at night. I'm hoping it continues to improve.

I noticed a difference in 2 days which is approx how long my neurologist had told me it might take. 4 days I was much better but I'm sure just like everything everyone's body will react differently.

My neurologist started me on 1 pill every 8 hours. My double vision did not go away at all. I took this dosage for 4 weeks. No change in double vision. Complained to him. He said take 2 pills every 8 hours. On the 7th day ... I woke up and double vision gone. Been taking 2 pills every 8 hours for about 4 months now.

When it is above 80 degrees. Humid. And I am working outside. I feel tired and rest a little (a nap). And, I might take a single pill (making a total of 7 pills for the day.)

Other Info: Get a good pair of sunglasses. Bright sun bothers me, Cloudy days bother me. Low barometric pressure bothers me. Driving during the day among trees where the light changes from shade to sun, bothers me. I choose not to drive at night. I ask my wife to do that. (But I do think I could drive safely at night, If I had too.

Summary: In my case... Mestinon did not work immediately. Only when my dosage was kicked up did I lose the double vision.

Hint: Avoid people that cause you the LEAST amount of stress. I find that my tolerance for dealing with ridiculous people ... has gone to zero. Don't know if that can be attributed to MG or is it a side effect of Mestinon.

Thanks for all the information. I do feel better on the mestinon. I can tell when it's time for my next pill. My voice and breathing are still affected by stress but much improved since Atari g the mestinon.