When a #GstTestClock is constructed it will have a certain start time set. If the clock was created using gstcheck.test_clock.TestClock.newWithStartTime then this property contains the value of the @start_time argument. If gstcheck.test_clock.TestClock.new_ was called the clock started at time zero, and thus this property contains the value 0.
Builder instance for fluent chaining
Set startTime property.