There's a scale in the manual that gives the operation capabilities/times per minutes charged in "direct sunlight", or other sources of "light". I can tell you that direct sunlight is much faster than anything else. I've only had one of mine go to "M" one time, but I try to put them in direct sunlight during lunch once a month and the rest of the charge comes from everyday wear. Winter months and long sleeves call for more frequent charges. But to answer your question, 3 days seems like plenty of time to reach "H", but I would try an hour or two in direct sunlight and see if that gets you there. (Use caution during summer months).
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