Holds last as long as they last. Use the fiction to determine how long that is.
If the Skinner hypnotizes you, she has a hold over you, because you have become obsessed with her. But what happens when the Savvyhead removes your memory of her and isolates it inside the psychic maelstrom? I would say her hold over you goes with your memory of her.
If you read a person in a conversation, your hold over her should be spent during that conversation. I mean, just because you scoped her out and figured out what's up with her that one time, doesn't mean the next time you talk to her you automatically know what's up now. Things change, you need to take another look.
But what if you are scrounging around the Savvyhead's lab, where she keeps all her notes and personal items, and you decide to read her through her stuff? Maybe you spend your hold while you are searching, while you are reading her notes. Like, you know she is going to check out the burn flats because the last entry in her notes is all about them.
Or, maybe you go and meet up with her afterward searching through her stuff, and you get to keep your hold, because when she lies about taking your memory away, you know because what she says isn't what she wrote in her notes. By scrounging through her stuff, you get to take your hold over her into a face-to-face conversation. But only if everybody agrees. Maybe the MC says no, you can only read a situation when you search through her stuff.
Those are just two examples that defy the usual guidelines: one where you might lose hold that usually sticks around, and one where you might get to keep hold that usually goes away. It just depends on the fiction. As long as your fellow players think you are reasonable, you shouldn't have too many problems.