It’s been a while, but I’m working on a big update to the main/free plugin and added a timestamp column to the signups database, which will be shown in a “Signup Time” column on the admin side views. The values will be shown as the date followed by the time, with date and time in the format that you set in your WordPress general settings page.
This will be in version 4.6, which I will hopefully release sometime in the next week.