Rasa-core, dealing with dates
I think you could have a validation in the custom form.
Where it perform validation on the time and perform next action base on the decision on the time.
Your story will have to train to handle different action paths.
I have a problem with rasa core, let's suppose that I have a rasa-nlu able to detect time  
eg "let's start tomorrow" would get the entity time: 2018-06-10:T18:39:155Z
Ok, now I want next branches, or decisions to be conditioned by:  

time is in the past  
time before one month from now 
time is beyond 1
month

I do not know how to do that. I do not know how to convert it to a slot able to influence the dialog. My only idea would be to have an action that converts the date to a categorical slot right after detecting time, but I see two problems with that approach:  

one it would already be too late, meaning that if I do it with a
posterior action it means the rasa-core has already decided what
decision to take without using the date
and secondly, I do know how to save it, because if I have a
stories.md that compares a detecting date like in the example with
the current time, maybe in the time of the example it was beyond one
month but now it is in the past, so the reset of that story would be
wrong.

I am pretty lost and I do not know how to deal with this, thanks a lot!!!