To see this, set "Samples to include" to include the whole day. Basically, determine how many samples MultiPing will have sent out by dividing the time period (8 hours, for example) you've been running by the ping interval. If you're doing 15 second ping interval, this would be 1920 for "Samples to include".
One way to help with this calculation is to use PingPlotter to help. If you're running PingPlotter with the same interval as MultiPing (which it sounds like you are, based on your other post), just enter "8 hours" into the "Samples to include" field. PingPlotter will determine how many samples that will be and will convert "8 hours" to a number (ie: 1920 for the previous example). This is in PingPlotter 2.60 only.