Hi Susmita,
The time interval is interpreted as minutes, the default is 360(6 hours), but you may set it to for example 1 day 1440(1 day):
repository.validation.delta = 1440
This defines the length of time for which a URL for content retrieval is valid from the time it was generated.
See the following KB article for details:
https://emcservice–c.na55.visual.force.com/apex/KB_How_To?id=kA5j00000008VYp
Regards,
Abderrahim