The +/- 15 minutes is correct but within 30 minutes of the filed EOBT, we deal with ATC who make any required changes to flight plans and slots........because we are in the aircraft not in the briefing room.
Unfortunately, our unit instructions states quite to the contrary. Whether this is line with the AIC that covered the matter I have not checked. Our instruction states that any deviance from the 15 minute tolerances is to be referred back to the pilot / handling agent / operating company to refile / send delay messages; unless the delay is caused due to airfield holding.
Anyone who calls me for a change will be / is told that they need to speak to company / handling agent. I would love to help and am able to do it myself but, when a completely un related incident happens 1 hour later, and the board find i dealt with it well, they will instead pull the extra assistance I offered to a frew who called at EOBT +16 out and slap me around the face for not following procedures.
In this non blame culture you must do everything by the book, otherwise you're screwed.
TIO