There really doesn't seem to be much you can do with the mosquito coils. Once you start one of the coils, the only piece of information you get is when it ends. If we immediately light the second coil, then we will succeed in measuring a two hour span, but that was hardly our goal.
Come to think of it, you could light one of the coils at both ends. That would let you measure a 30 minute span. But...then if you lit the second coil, that would measure an hour still.
But suppose you lit three of the four ends of the coils? The coil that was burning at both ends would be used up in 30 minutes. There would be 30 minutes of burning left on the other coil. But now if we lit the other end of that coil, it would burn up in just 15 more minutes. Making a total of...45 minutes.
Run the 13 minute hourglass. Then start the 13 minute hourglass and the 9 minute hourglass. After 22 minutes, the 9 minute hourglass will be empty. Start it again immediately. At 26 minutes, the 13 minute hourglass will be empty, and the 9 minute hourglass will have... 5 minutes of sand remaining, and 4 minutes of sand expended. Immediately turn the 9 minute hourglass. This means that at 26 minutes, you now have the 9 minute hourglass with 4 minutes of sand remaining. This will empty exactly at the 30 minute mark.
Back to the Timer Puzzles.