Not a permanent change. Amtrak is working with BNSF. BNSF is replacing a lot of ties. Next Friday the SL will leave at 10. on April 4 the SL will be leaving at 11:59 again.
The later departure is not Amtrak's choice.
When I left LAX at 8PM on Friday Feb 7, we sat at Maricopa for 1:40 in order to leave "on time". We still got to TUS early.