It is hard to know the "right time", personally I trusted my gut and I am very happy with both contracts!
I did a lot of stalking here on the ROFR thread, and that gave me an idea what I'm willing to pay. I also stalked the broker sites daily!

Now here is the catch - Are you adamant about UY and the amount of points? If you're looking for very specific contract (aka your own unicorn contract), you might have to give in even if it's a little higher than you want to pay. Vice versa, if you're more flexible, that gives you more time to look for a good deal.
Also remember this, don't get too hung up on those unicorn deals that people posted, they got lucky but that shouldn't be used as your "guide/standard" for a good deal. Hope this helps!