I did the ladder exercise first too when I started. I only imagined for 3 days, at night I visualized climbing the ladder, and then forgot about the exercise entirely. Almost 2 weeks later I climbed a ladder for the first time in my life and had to climb it many times after.

I think the issue you're facing is that you're too much concerned about the outer results. You're imagining and then looking outside for results. The 3D (External world) should not be your main focus when it comes to manifesting. It's only a mirror that reflects what's happening in your 4D (Internal World aka Imagination aka God). Your imagination is the true reality, What happens in imagination is the truth. If you're a beginner it may be a little difficult to have faith in your imagination since you haven't consciously used your imagination to manifest anything yet but the only thing you need to do is have faith in your imagination, that is the only requirement,

The way I would go with this is to,

Imagine for 3 days, no less or more, before in bed, Visualizing climbing a ladder.

After 3 days, I stop imagining the ladder and go on with my life. I know what I have imagined is inevitable and I am bound to encounter it in my life sooner or later. Since the 3D is a mirror which always reflects what I have imagined.

When will it happen? I don't know and I'm not concerned about it. It could happen at literally any second, It's not my headache to predict when it will happen. I have better things to tend to.

Will it happen? Absolutely, There is no doubt about that. If it were not to happen then that would mean that the Law is a fraud which it isn't, (I have seen the Law works thousands of time in my life.)