Henna colour saturation: dilution with cassia vs. less time on.

[Nocturnal]

So this is a henna newbie question from me.
The more cassia you have in the mix the less dark and less saturated a henna stain will be. Also the less you leave henna mix on hair the less dark and saturated it will be. Is it possible to get the same result as with henna-cassia mix if you leave straight henna on for less time? Or do you really have to leave henna on for long time or the hair colour won't come out even? What is the general understanding on this?
Please pardon my English, for some reason I have difficulty making sentences (and sense :D) today. Thank you!

[Nightshade]

I consider there to be a more forgiving margin of error for a cassia/henna blend than a henna straight mix.

For instance, I've left my cassia/henna blend on 3-4 hours on accident once (normally only for two) and it was not significantly darker than normal. The same mistake with henna would be VERY hard to reverse.

And cassia being less expensive than henna (or even just diluting the henna with conditioner) you save money that way too :)

[Nocturnal]

Nightshade, thank you for your input! I was thinking to cut down time since I'm not very patient, but now I think you are right in terms that a risk of letting henna on for too long is not worth it since henna is very permanent and irreversible.