I'm not sure why. I'm pretty sure OP_CSV (relative to the input it's spending I believe) and OP_CTLV (absolute) would allow you to do this.

I know a lot of mempools will reject non-standard transactions and this might fit the bill, but idk.

Here's a really good article on time locks for anyone interested: https://medium.com/summa-technology/bitcoins-time-locks-27e0c362d7a1