You might be unavailable at a particular moment to send an email. Simply schedule your email using gmail.
Here’s how to do it.
⦁ Click on ‘compose’ to compose a new email.
⦁ Tap three dots on the top right corner.
⦁ Tap ‘Schedule send’.
⦁ From the available options, tap ‘Pick date & time’.
⦁ Enter the desired date and time and tap ‘Schedule send’.