A checkbox has a linked cell, which contains the True/False representing the state of the checkbox. It is much easier to reference this cell's value than the value of the embedded object which is the checkbox.
Manually: Right click on the checkbox, choose Format, click in the Linked Cell box, and select the cell to contain the checkbox value.
In code:
Set cbTime = ActiveSheet.CheckBoxes.Add(100, 100, 50, 15)
With cbTime
.Value = xlOff ' = unchecked xlOn = checked
.LinkedCell = "$A$1"
End With