Hi Jen,
So you are now on 60 mg Mestinon 3 times a day. If it doesn´t fit your needs, there should be no problem to take Mestinon 4 hr apart as most of us do.
Neuro´s are usually cautious with newbees and increase the dosage slowly but you will quickly learn to listen to your body and adapt your dosage according to your activities and condition.
Be always cautious and modify only one parameter at any one time and I you don´t feel well, go back to your previous dosage.
Working with the time interval is always preferable to modifying the dose which you should not do without your neuro´s approval, but increasing the frequency to 3 hrs or 3.5 hrs is ok.
When you modify something and find yourself better, keep your neuro informed so he knows how you react to medication.
And for steelworker, time span is for MG´ers with generalized MG (general muscle weakness), as southblues said, so that they can breath during the night, swallow their pills in the morning, have a normal breakfast and then live through the day with normal mestinon.
I hope this will help you build safely your own experience.
Maurice.