I'm working on a survival analysis for patients undergoing cancer treatment. To account for immortal time bias, I want to perform a Landmark analysis.

I have a variable that provides the survival time, from day of diagnosis to last follow-up/death (var: DX_LASTCONTACT_DEATH_MONTHS).
I have a second variable that provides the time from diagnosis to first "treatment". (var: DX_RX_STARTED_DAYS)

I want my landmark time to be the the day of first treatment. As a sensitivity analysis, I want to also set the landmark time to 30 and 90 days.

My code is:

stset DX_LASTCONTACT_DEATH_DAYS, failure(PUF_VITAL_STATUS==0) origin(time DX_RX_STARTED_DAYS)

For the 30 and 90 days:

stset DX_LASTCONTACT_DEATH_DAYS, failure(PUF_VITAL_STATUS==0) origin(time 30)

I can't really figure out if I should use "origin" or "enter" to perform the Landmark analysis. I've read the manual and can't really figure it out.

What is the correct code: "enter" or "origin"?