for a very important date. (No! Not that!) I'm late setting the sundial.
Today is the Summer Solstice so it would make [some] sense if today were the day, but where I live the sundial should have been "set" last week on June 16.
Remember a day when the world did not operate on nanoseconds and digital technology? A day when the navy rang bells to mark the passing of the hours, monks burned calibrated candles, and folks used sundials - at least during the day. For most of us today a sundial in the garden is nothing more than a decorative object.
I'll spare you the boring details - most of which I have forgotten - but if you want to set your sundial exactly you need to know what day [closest to the Solstice] the sun crosses over "your" meridian at exactly noon. If you are in the exact middle of your time zone, then it would be today. If you are east or west of the middle then it happens early or late. How many days either way depends on how far east or west you are. It all has to do with the tilt of the earth, and its wobble on its axis, and a bunch of celestial navigation issues.
Since "close enough" is fine with sundials, then do it today at the Solstice. Or, tomorrow. All you have to do is set it at noon [sun time not Daylight Savings!] so that the shadow from the gnomen is exactly on 12 or XII. It will stay pretty accurate for the rest of the summer, but after the fall equinox it will begin to be noticeably "off".
Lest you think I am a total slacker, I did try to do it on the 16th. As luck would have it, tho, that was the only fully overcast [read cooler] day we have had in two weeks - not enough sun to cast a shadow! The next two days I had to work offsite - don't you hate it when work interferes with fun? And, then we had company all weekend and weren't around at noon. So, today was the first chance that I had to do it.
Now I'm good to go for a while.