Google-sheets – Data Validation in Google Sheets Using Multiple Criteria

I have a column with text in the format:

[text:more text/numbers]

I want to ensure whatever is entered into the cell conforms to this syntax, or at least as much of it as possible.
text is always 5 characters long and capitalized. The part after the colon is of variable length.

Currently, I am using simple data validation to check that the trailing ] is in the cell. The criteria are Text contains ], rejecting input for everything without the ].

Using an IF statement, could I check the cell for those symbols/string lengths and reject everything that doesn't conform? Ideally, I would use the formula within the data validation feature, rather than as a script, for example:

Criteria: Custom formula is =(FORMULA HERE)

Any ideas would be appreciated on this.