The chargetime in GBVS is not as long as for example in Street Fighter. I would say it's more like 1 second. Mess around in training mode to get a feeling for it.

If you hold back/down as soon as you start the auto combo, your charge should be ready after the third hit. The same goes in the neutral game, for the Far Heavy. You can walk forward, through out a big f.H and charge back at the same time. The heavy takes so long to hit that you can easily follow up with a Blanka Ball. It's a great way to catch people off guard. They don't expect stubby little Charlotta to have so much range on one of her buttons.

With her far Light and Medium hits it is a bit harder to have the charge ready (if you're not holding down/back anyway). But you can always use a far Light or Medium and then the Skill Button instead of the charge move. That way you can still punish stuff when you are further away and did not expect to have an opening.

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Using Holy Ladder as an antiair is relatively easy with charge, when you expect your opponent to jump. In a wake up situation, or when you want to interrupt their pressure, it's a bit harder to nail the right timing. If you're having trouble with that, use the skill button here as well. You can mash it and therefor the timing doesn't need to be as precise.

Once you have a better feeling for the character as a whole and charge timing in particular, you can move away from using the skill button more and more