In the event that you don’t have a VAT-ID during your first job, VAT will not be invoiced for this job. You don’t have to declare this job in your turnover tax return. The reason for this is that you are still looking at whether entrepreneurship is something for you and if you have the intention to become an entrepreneur, so you don’t need a VAT-ID yet.
Note: you do need to state this income when declaring your income tax.

Do you make use of the Small Business Scheme? In that case you won’t receive VAT for your other shifts either. You don’t have to declare your VAT.