My granddaughter is 18 months old and has used about 5 or 6 signs for months now, and is just starting to talk. Just like babies aren’t born speaking, it takes time for them to use basic signs but the muscles movements in their mouths needing for speaking take longer to develop that skill so the sign language really works to help them communicate basic things.
Yes, it will take time but if you’re consistent in using them whenever you ask them simple questions or give simple statements, they will pick it up.
I’ve never seen my granddaughter have a tantrum for things other kids scream about, like wanting “more” of something or needing “help” with something. It gives them an early tool to communicate needs or wants because they understand much of what we say but can’t respond so this gives them some options while their facial muscles develop.
They may use their own variation of a complex sign or two but you’ll soon catch on to what their version means because they’ll be consistent with it and based on what they’re doing when they use their version. My grandaughter taps the top of her wrist with her other hand for help, for instance.
The goal isn’t perfection, its helping them communicate in a way they can manage to minimize frustration all round.

Was wondering the same thing.

Try sticking with one sign at a time. We started with More, it does take awhile for them to pick it up. My son has his own version of more but I understand what he means and show him the proper sign every time. He will be 15 months and he knows more, and milk. He will do All done some times but I’m working on that one. We also started eat, help and water.