Thus theres no returning within a short time (4)
I believe the answer is:
soon
'time' is the definition.
(thesaurus)
'thus theres no returning within a' is the wordplay.
I cannot quite understand how this works, but
'thus' could be 'so' (synonyms) and 'so' is present in the answer.
'no' could be 'o' (resembles 0 - 'no' can mean 'zero') and 'o' is present in the answer.
A single letter 'n' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'short' acts as a link.
Can you help me to learn more?
(Other definitions for soon that I've seen before include "Presently" , "Willingly" , "Before long" , "Early, in a short time" , "Before you can say Jack Robinson" .)