Shouldn't it be "would" instead?

I think there are a couple of ways to do this depending on whether this past tense or not.

"He explained that if the beneficiaries are informed that their accounts will be frozen, they would have ample time to transfer the money out of the accounts elsewhere."

"He explained that had the beneficiaries been informed that their accounts would be frozen, they would then have had ample time to transfer the money out of the accounts elsewhere.

Thanks, engineer.