I check the spreadsheet that has a column with a header as Simple time. What is simple time? I don't check but I guess you meant it is GMT time. Even if it is GMT time, you should edit the header to GMT time. If it is another time zone, you should also edit it with appropriate time zone.
I checked it with
https://www.epochconverter.com/, your Simple time is GMT time.
The first one in your spreadsheet, is at 1436270000 (UNIX) ~ Tuesday, July 7, 2015 11:53:20 AM (GMT time)
One more suggestion, you should differentiate past checkpoints and future checkpoints by different colors in the spreadsheet. It saves time for readers to find the next checkpoint.