The time needed for the component to be carried from the burner tip to the observation space (in s). Travel time depends on the observation height and the flame rise velocity.
Source:
PAC, 1986, 58, 1737. 'Quantities and units in clinical chemistry: Nebulizer and flame properties in flame emission and absorption spectrometry (Recommendations 1986)' on page 1742 (https://doi.org/10.1351/pac198658121737)