I regularly get meeting and time requests in my email from my colleagues and occasionally from students. I use Airmail to manage my email on my iPad and iPhone because it has the share button. The share button allows me to quickly and easily process my email by sending email text and data to other apps such as Workflow. Since I can share the email to Workflow, I built an Action Extension Workflow that gathers the text of the email and puts that in the note section of the calendar event. I input start and end times and then I have the calendar entry finished.
Workflow link: Email to calendar