searched for related posts and saw several people get 2-week grace period so happily called BAEC line to ask for an extension of 3 days, hoping to hit 3500 points.

After consulting with her manager, the agent told me this is not possible as per BA policy, grace period will only be granted to customers who want to reach silver/gold tiers, on case by case basis. It cannot be granted to those who try to get 2500/3500/5000 points.

to be honest, this is fair enough as I was trying to ask BA for a favour. But I don't see why trying to get 2500/3500/5000 points is treated diffrently compared to trying to get 1500/600 points.