Rancher devops docker file build time is same again and again

Hi ,
I have created the stages for the rancher devops pipeline for building the docker images .
The time calculated for the first time build stage is around the 35 minutes and on re-initiating the build the time taken is again same rather it should be lesser as the build is already been done first time . Please confirm if the build will always be same in the rancher pipeline build or it should be lesser on build stage doing the second or further time .