Can I reply from my phone after 24 hours?

In AFRUS, not with free text. WhatsApp Business works with a 24-hour window counted from the contact's last message:

• Abierta (expira en …) (Open): less than 24 hours have passed; you can write free text.
• Cerrada (Closed): 24 hours or more have passed; you can only click "Enviar plantilla" (Send template) and choose an approved template.

If the contact replies, the window opens again.

Keep in mind that the number can't be linked to any other bulk messaging service or have a WhatsApp Business account associated with it. If it is, when you connect it to AFRUS, Meta will say the number is ineligible and you won't be able to connect it.