As long as your number remains active with your current provider, it's unlikely that you will experience any down time. If your current provider doesn't disconnect your number after releasing it to us, there shouldn't be any interruption of service on your line.
Your current provider still has control over the number until the transfer process is completed on both ends. If the line is not working before the date of completion, contact your current provider to re-activate it.
Toll Free Numbers:
If you're transferring a toll free number, it’s unlikely but possible that your number may be temporarily unavailable during the final stages of the transfer process (depending on the providers involved). Please make sure that you keep your former provider account active until the transfer is completed.