There are 2 important alchemist transmutes which currently resets at 00:00 server time, these are Transmute: Truegold and Transmute: Living Elements.
The Truegold transmute gives, as the name suggests, Truegold. The Living Elements gives 1 of the 4 of the types of Volatiles - life excluded - usually this is turned into Volatile Air.
There're many gamers that are up at 00:00 server time, and most tend to post their auction before they go to bed in hope of it to be sold the next day. This mean, that the price will fall significantly at the night, but will increase dramatically (~100-200% increase) doing the day.
An example to this is that I bought ~100 Volatile Airs @ 30g each (3000g) at 4:00 AM server time, then the next day, about 12 hours later, they were 60g each. At 8:00 PM they were 80g each, and kept rising until it hit 00:00. I sold it at 60g each, which was a 3k gold profit done with barely 10 minutes of work.
And really, don't be afraid to buy the Volatiles - especially air - as they're used for pretty much everything currently, resulting in very high demand, which makes them very easy to sell.
Hope it helps.