I've set mine for 4.5 hours after sleep, 5 hours, and 6 hours after sleep for WBTB alarms, on different nights of course. Be careful not to get too used to it - the idea is to inject a little awareness into your sleeping mind by waking it up and letting it go back to sleep, so it doesn't stay too unaware in dreams. Therefore, it needs to have the right amount of sleep first, then you can set your WBTB alarm for whenever you suspect you're about to begin dreaming a lot, which will come after the 4.5 hour mark of sleep. You'll need to experiment, there's no two ways about it, but that's what I've set mine for in the past. It works great for recall, as I see you've found out.