One of the more interesting legacies Night Below has bequeathed to D&D is the glyph-magic of the aboleth savant, as seen in its 2e-format "Monstrous Compendium" supplemental insert.
Carl Sargent's four master glyphs covered a given area for an indefinite amount of time, in which people would suffer the effects until they left the area. Wolfgang Baur's glyphs, master or not, remained dormant until someone touched them, at which time the glyph would loose its fury on the victim (or his/her party).
In the Creature Collection's "Fiend Factory", Scott Greene and Erica Balsley erroneously declared the Glyph of Enfeeblement a Baur-style dormant glyph. In their defense, Enfeeblement could certainly be used as such. Likewise, some one-shots would be very powerful if cast as continually-active area effects. A permanent Nightmare, as an example, might reside in a minor corner of the priests' chambers, disguised as far as possible. This could potentially warp a population for generations.
Greene and Balsley further decided to limit the other Sargent glyphs' duration to one turn per level of the caster. The DM can decide where this applies in principle; but I assume that where a glyph is employed according to Sargent's template - that is, ambient - the glyph's area-of-effect lingers until dispelled.
4 August 2001: figured out that there was a difference between variants of Nightmare Glyph. 17-18 August: moved that variant into a separate section. 17 Dec 2005: moved the glyph-specific information to this new page.