U. = Until (e.g., "until dispelled", "until broken", etc. in OD&D)
OD&D doesn't have a standard “Duration” stat block, so one must parse out details from the text when available. Thus, you'll see a lot of variation in OD&D the descriptors above, such as "until dispelled" (usually equivalent to "Permanent" later on), "until broken" (as by special rules for charm or invisibility spells), "until contact", etc. The few “N/S” entries above are in many cases the same as “Instantaneous”, although a few of those spells are presumably very long-lasting (wall of ice, magic jar, control weather).
I've also added a column for S&S, that is, Gygax's Swords & Spells miniature combat rules for use with late-era OD&D; this work includes a comprehensive "Spell Chart" on p. 12-15 with a listing for Range, Area, and Duration for almost every spell in D&D -- sometimes with updates or fill-ins to spells that previously had no specifications for those elements (thanks to Zenopus Archives for reminding me of that). One thing to look for here is that Gygax uses a dash ("-") for both instantaneous spells (fireball, lightning bolt, teleport, etc.) and specially long-lasting spells (charm person, charm monster), and I've also been using a dash for spells missing from a given edition (for S&S: read magic, read languages, telekinesis, legend lore). Gygax specified "until dispelled" both for spells limited in the text by concentration and those that were literally unending (e.g. makes wall of fire and wall of ice look identical when they weren't in OD&D Vol-1). Also note: the newly-minted duration for sleep (4-16 turns), reductions to clairaudience/clairvoyance, and some minor changes (or typos?) to ventriloquism, detect evil, and ESP, that were ignored in later editions (including Holmes Basic, B/X, etc.).
Note on this point that the Moldvay/Cook B/X rules are the first to actually list spell durations as "Concentration" or use the word "Permanent". (Even Holmes Basic uses the description "infinite" in any of these cases; see continual light, invisibility, magic mouth, phantasmal forces, and wizard lock).
As we look at later editions, here's a very rough correlation of duration categories:
- OD&D 2-3 turns → AD&D 1 round/level → 3E 1 round/level.
- OD&D 6 turns → AD&D 2 rounds/level → 3E 1 minute/level.
- OD&D 12 turns → AD&D 5 rounds/level → 3E 10 minutes/level.
Anything else that you can spot here of interest?