What do you envision. Typically you share something and people stop looking at it as it dissapears over time. This is natural on Nostr.

Instagram has an advantage of providing access control: only certain people can see it.

That gives the time element a bit more exclusivisity.

Also, since cryptography has no concept of time, this is the only way to do this but nostr is a cryptographic protocol, not a man gated platform.

We can create clients that simulate the behaviour which is probably what whatsapp does. It could allow you to set an expiry date and clients will ignore the post after that.

Does that work for you?