...creature cannot have died more than 24 hours prior to the casting of this spell.
Can you cast `Gentle Repose` on a corpse to extend the 24 hour requirement on a corpse for this spell?
School divination Level bard 2, druid 3, ranger 2, sorcerer/wizard 2
CASTING
Casting Time 1 hour
Components V, S, M (powdered metal and rare inks worth 100 gp)
EFFECT
Range touch
Targets one dead creature
Duration instantaneous
Saving Throw none Spell Resistance no
DESCRIPTION
You can take a piece from a dead creature's body and use it to create a map that reveals the locations of any valuables that creature knew about while still alive. You must cut this piece off yourself and the creature cannot have died more than 24 hours prior to the casting of this spell. You cannot cast this spell on a creature without a physical body, and the portion you remove must have a fairly level surface such as a piece of hide, carapace, or skin. The map you create is accurate to the best knowledge the creature had at the time of its death. It reveals the location of one source of treasure for every three caster levels you possess.
Any inaccuracies or faulty information held by the creature are represented on the map as well. Similarly, the map cannot account for any changes that occur after the creature's death.
You must choose the scale of the map when creating it, opting between nearby (e.g., one or two dungeon levels), local (e.g., a valley or community), or broad (e.g., a country or larger). The map reveals the locations of what the creature deemed most valuable within its area. Depending on the creature, the map might reveal a source of tasty food, suitable mates, or even your own treasure vault.
and
School necromancy; Level cleric/oracle 2, sorcerer/wizard 3
Casting Time 1 standard action
Components V, S, M/DF (salt and a copper piece for each of the corpse's eyes)
Range touch
Target corpse touched
Duration 1 day/level
Saving Throw Spell Resistance negates (object); Spell Resistance yes (object)
You preserve the remains of a dead creature so that they do not decay. Doing so effectively extends the time limit on raising that creature from the dead (see raise dead). Days spent under the influence of this spell don't count against the time limit. Additionally, this spell makes transporting a slain (and thus decaying) comrade less unpleasant.
The spell also works on severed body parts and the like.
It looks as though RAW the intent is clear that the Create Treasure Map spell says 24 hours since its death. While Gentle Repose makes the extension of the time where one may raise the body, it does not change the date/time the creature was slain.
However, it could be ruled by a generous DM that it could help.