Within a stasis field, time slows or stops for the affected items. It is apparent that the affected area is able to be penetrated with light in the visible spectrum (and so should be able to be penetrated by other EM radiation), but physical force doesn't work, so it probably can stop particulate radiation forms. It is also apparent that the entire stasis affected area is able to be moved by outside force.
Memory Beta (the non-canon Wiki) has an entry noting that a DS9 novel used stasis fields, as well.
Stasis fields of various kinds also appear in the Animated Series; in More Trouble, More Tribbles, the Klingon one has an effect solely upon ship systems; the crew remain able to function and to direct robot freighters outside the field. BEM has a similar effect via a non-corporeal being.
In The Slaver Weapon, we get the following:
SPOCK: These stasis boxes are the most remarkable thing the Slavers ever produced. Time stands still inside a stasis box. A billion years means nothing in there.
There are stasis field references in TNG:
Man of the People,
Face of the Enemy,
TNG Movies: Insurrection
There are references in DS9:
The Die Is Cast,
There are references in Enterprise:
Home (as a kitchen appliance),
Cold Station 12 &
The Augments (as lab equipment)
Other Voyager references:
Equinox (Alien ones that are multi-purpose),
Blink of an Eye,
There are other referenes as well; I'm not going through every transcript.
Suffice it to say, however, that various forms of stasis generators of various efficiencies and specific effects exist in Trek Canon, and not all are the same effectiveness at time slowing, not all affect all material inside, and the Slaver one in TAS is about the most efficient one.