Yes. Buy does the spell affects everything within the ring at the time of casting, or everything within the ring while the ring remains unbroken? In other words, once you have turned the army into statues, can you walk amongst them without being assulted by the spell?
I would personally allow both versions - the one that affected only the targets within the the circle at the time of casting, and the one that affects anyone as long as he is within the circle, but not apporve of a spell that affects only the ones present at the time of casting whenever they are within the circle.
Looking over the rules, I think it doesn't but it is a "loophole" of sorts.
You still only affect the present. No violation of the limit of time per se.
You do change the body of the person to stone, which ages differently from flesh, so may circumvent the limit of aging and fatigue to some extent. But following the example of the silet vigil, you apparently do age normally and only slow fatigue gain.
My suggestion of frozen time amounts to preservation, yes, but not slumber nor considerable safety. I suggest that effectively no time passes while in stone form - so no sleep is being accomplished, no perceptions are being sensed, no thoughts are being thought. A Me requisite, in retrospect, seems necessary.
Regardless, the rules do not seem to borne this idea out. Stones do have minds (the mind that sits), and so feel the passage of time. Perhaps a spell that turns a human into stone in body and spirit would allow slowing down aging as well as thought, in comparable amounts, bending the limit of aging to some degree.
I would think that preservation of food by transforming it into another substance would be appropriate, indeed. In general I do not believe it beyond Hermetic magic or even difficult, it is a variant of charm against putrefaction which is but MuCo 10. Turning food into another substance is simply another way of accomplishing this goal. I feel that a rope turned into bronze has the qualities of bronze, and does not "age" as a hemp rope does. I confess that the silent vigil throws that into question, if you consider food spoilage as "aging"; I maintain this is for game balance reasons and should be considered to apply to humans, not to the rotting of food.
A Stony Existence
MuCo(Te,Me), R: Personal, D: Ring, T: Ind
This spell transforms the caster's body and mind into that of a stone. The caster becomes motionless, a stone figure. His mind and perceptions slow down to those of a stone, although he is still recognizably himself.
The magus's time effectively slows down by x10. He can still nonritual spells, without words and gestures, but it takes him 10 times as long to do so. He still ages, but he does so at a rate ten times more slow. He still gains fatigue (although not body) levels from his complete rest, but at 1/10th of the normal rate.
With an appropriate magical effects, the magus may be able to sense and move enough of the world around him to engage in laboratory or other activities. These, too, are done in 1/10th the speed, so he can only learn 1 season's worth from a book in 10 objective Seasons. Engaging in non-mental labwork, such as investing or preparing items, requires working in accordance with celestial times and is hence more difficult; apply -10 to the magus's lab total should the SG determine astrological correspondences are relevant to the work at hand.