Seems like taking images is fine according to the document. But still, I was once accosted by an LP of Manwar Sangam Express out of all trains for taking images. In either cases, I don't think you have ever had RPF question you for near an hour because you were photographing late at evening in the yards :p.
The LP bothering thing made me remembered when I stupidly went into the yard at late evening. Got some good images but really had an issue with RPF personnel. The original half decade old post is here/blog/post/1838510
yes I mostly go in morning and evening time only
Mau, not having a very big yard, I can rarely spot any RPF there, even at PFs they are not so many
Mau also handles freight on daily basis (yes, almost daily a new rake gets placed, so I can always spot various freight locos :) ), beside line number 8 (goods handeling area) there are always trucks + men in huge number, so no-one (neither RPFs nor pax) could get from Platform that someone is taking pics.