Yes, chances are that, with a Debt Management Plan, you will be paying your debt off over a longer period of time.  This is because you will be making reduced payment to your unsecured creditors and some may not freeze the interest and charges on your debt.
However it is important to remember that you will no longer to struggling on a month to month basis as your debt repayments will be affordable to you.
An IVA is slightly different. The length of an IVA is typically 60 months, at the end …