You could use it to make some timed or remote explosives/poisons/other nasty things. I'm not a chemist, so I'll leave some of the exact formulae to someone else. But the basic idea is:

-Start with something deadly.
-Stabilize it with something you conjure.
-Place it wherever.
-It will explode/light on fire/become toxic/etc. after 1 hour, or when you use the ability again.

One formula I do know:

NaOH plus hydrochloric acid = saltwater. Start with a volume of hydrochloric acid. Conjure just enough NaOH to turn it into salt water. You can now turn it back into acid on command. I'm sure a creative player can find all sorts of uses for timed/remotely triggered acid charges.

Etc. Etc.