Yeah I did a fair bit of reading on the subject and came to the conclusion a 0 minute no chill addition is about equivalent to a 15 minute addition.Calculating late additions for no chill is a bit of a dark art, and hard to get from brewing software as there are a lot of variables (cube volume, wort temp, type of hops, ambient temp etc).
Best way is a bit of trial and error to work it out for you're gear and cube sizes.
Most people calculate the IBUs added from cube hops/late hops as somewhere between a 10-20 minute addition.
FWIW, when I make a hoppy beer I put in a bittering addition at 60 minutes (with about 20-30% of the total IBUs), then put a huge cube hop addition to make up the rest of the IBUs + the flavour. I calculate it as a 15 minute addition, and it works brilliantly for my setup (old 17L fresh wort kit cubes). Great smooth bitterness and amazing late hop character.
The other option is do a mini boil with about 5-10L of wort and use that for your late hops (search for Argon's method). You can rapidly chill the wort in a sink of iced water, the strain the cooled wort into a fermenter with the rest of the cubed wort.
You should be able to nail down what works for you in no more than 2-3 brews.
When I first moved to no chill recently i just moved my 10 min addition to the cube and 0 min to a dry hop. I pretty much fluked a good method for the American Pales and Ambers I usually brew. It ended up with similar bitterness, a bit less but counteracted with a bit more hops in the cube addition.
I guess like a lot of brewing its a bit trial and error. However it takes the accuracy of brewing software and makes it much more seat of the pants. Calculated IBU's are already somewhat questionable and this just makes it more so.
However the time and water savings from no chilling have been more than worth it for me. Next time I do an IPA or similar with multiple hop additions at different times I will probably do a tradition rapid chill however.