You can setup punch reminders using AttendanceBot dashboard for your team

You can specify the time for both punch in and punch out reminder. This reminder would go to all members of the Slack team at their respective local time.

Here is what a punch in reminder looks like.

To enable the punch reminder

1) Head to Settings-> Basic Settings and scroll down to the Time Settings.

2) Switch the toggle from "Inactive" to "Active"

3) Click on the edit icon and add the punch in/out time. 

Note:

You can also choose to automatically punch out people (as opposed to simply reminding them of it by enabling and setting an "Auto Punch Out" time). 

Here's an article explaining how you can setup auto-punch out for your team