Short answers about how calculated fields behave.
Q: When are custom calculated field values actually calculated? A: Instantly.
Q: What programming language is used to create custom calculated fields? A: C# (C sharp), consistent with validation rules.
Q: How many custom calculated fields can I create? A: Each Insightly instance can create up to 20 custom calculated fields per object.
Q: Can I create a calculated field that contains other calculated fields? A: No, this is not currently possible. Formulas cannot be layered; each must stand alone.