This isn't possible. You can control when you start the 24-hour SMTP retry period, but you can't abort the retries based on a time window.
On the other hand, you shouldn't need constant retries for a significant part of your database. What percentage of your leads (you called them "customers" — is that accurate from a sales standpoint?) are having this problem in a given send?
Also, I wouldn't use the expression "Soft Bounce" to refer to messages that have not, and will not, bounce. They're simply being retried and if they fail, that's your bounce.
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