Where can I find market volume data with greater resolution than 24hr periods?
You could do your own price comparison.

So if you scrape every 15 minutes. Store that 15 minute price data and create your own percentage based on the history of the data you collected.

If you have the data every 15 minutes you could even do the difference in 15 minutes intervals.

Example:
Price now is $1.00.
Our database says the price 1 hour ago was $1.15
Change of -13% over the past hour.

Again, store all the 15 minute scraping price data in your database and then use that data to make the percent based on whatever time frame you want.