It depends on how much data you're going to burn, and how fast your drive is. Burning 650MB of data takes about 74 minutes at 1x, 37 minutes at 2x, and 19 minutes at 4x, but you have to add a minute or two for "finalizing" (sometimes known as "fixating") the disc. So, burning 700MB of data takes about 3 to 4 minutes at 52x with "finalizing" the disc.

If you have half the data, it will finish in (about) half the time.

Remember that single speed is 150KB/sec, double speed is 300KB/sec, and so on.