That kind of depends on a lot of things. I'm writing up a bunch of changes to rotationals and stuff right now.
First off, the only way to have the shard generation for between 50-70% uptime on UA. Its literally impossible to maintain a 100% uptime because of our shard generation rate, so you have to pick and chose when you want to put up UA.
- You NEVER want to cast UA without reap. This is a 10% damage buff + What ever modifiers you would have to UA (Perdition, Shadowy Encantations, Inherently Unstable).
- You want to make sure you have enough dot time to get some good drain time with the contagion buff. This also means you get maximum drain time during Reap up-time.
- you would LIKE to have some stacks of CH
- The soonest you would like to cast a new UA is with 1 tick left on the old reap.
Notice theres a few changes here (I will be updating the guide shortly). Theres a balance that you have to strike between contagion uptime and good damage on UA. Also, if you are using the heirloom trinket on Demons (which is BIS right now even on non demons), you REALLY want to try to have 2-3 shards in reserve for when a proc happens. So with this trinket you will want to shift things down towards getting the maximum UAs outside of trinkets to prevent wasting things like CH.