È poco probabile che riesca a finire questo lavoro
It is not very probable that I will succeed to finish this work until this evening.
Non credo che si possa leggere questo libro
I don' t believe that this book can be read in one week.
In relationship to an instant of time there is no problem.
Urgente, devo scegliere
not: Urgente, devo scegliere in domani.
Urgent, I have to make a decision until tomorrow.
If entro is used with a period of time the meaning is within.
within a period of time
Lo posso fare in / entro un' ora.
I can do it within an hour.
after the period of time has passed
Lo posso fare tra / fra un' ora.
I can do it in an hour. (After one hour has passed.)
If you want to express that something is going to happen after a period of time you have to use tra / fra.
tra / fra
I do it in one hour.
(=> I do it after one hour will have passed.)
in / entro
I do it within an hour.