Short-Term Vs long-term survival

[Joe]

Hi

I am running a known fate analysis to access survival after release.
I want to estimate short term survival (three months after release) and long term survival (more than 3 months of release), in addition, I want to access the effect of some covariates on both short term and long term survival.

My question is how to build a design matrix to measure the effect of covariates on long-term and short-term survival separately? do I need to run two separate analysis?

Thanks
Joe