It's definitely post-Heart Of Gold. Robin is already married to Marian and stealing again. Considering Regina cursed herself to be barren, I would say this is shortly before the events of True North. By her twisted logic, if she couldn't have children, no one could, and so she'd steal children to send into the Blind Witch's house to get the Apple. Until Gretel so impressed her, she wanted to adopt her and Hansel. Since True North is also contemporary with 7:15, this would place Mother between Snow Falls and 7:15/True North. It would also help solidify the belief that Hat Trick is after True North. (My personal belief is that Hat Trick is closer to the middle of the timeline, around An Apple Red As Blood.)
I've Tweeted Jane Espenson to ask if this is indeed when Cora kidnaps Henry and whisks him away to Wonderland, but either way, this also helps clarify Wonderland's timeline a bit.
In "To Catch A Thief", Cora has all of her forces chasing Alice, but she herself is nowhere to be found. I would wager that "Mother" and "To Catch A Thief" are concurrent, as Cora says she used the White Rabbit to get to the EF, meaning she'd have him in her posession once she returned to Wonderland, and near the end of TCAT, Will appears in Cora's maze with the Rabbit, giving him to Alice. Suggesting he stole the Rabbit from Cora around the time of her return.
(This also means that Alice and Cyrus' love story takes place roughly the same amount of time that Snow and Charming's does.)
tl;dr Snow Falls/Snow Drifts/There's No Place Like Home ---> Mother = To Catch A Thief ---> True North = 7:15 ---> Hat Trick