Scheduling in the Gmail or Outlook app on your phone uses that app’s own feature. HawkOpen does not add tracking to an email sent that way, so it is not tracked.
To schedule a tracked email, write it in the HawkOpen dashboard, pick the date and time, and confirm. It is sent through the Gmail, Outlook or IMAP/SMTP mailbox you connected. The browser extension sends right away and does not schedule.
The Free plan does not include scheduled sends; they start with Pro.