You need to start a new Audacity session and to load the audio you want to add regularly-spaced labels to. Select audio [control+a]. Open analyze menu [alt+a]. Click on 'Regular interval labels'. use or change the following five default variablees:

1. Label interval [seconds]
Default sixty seconds between labels, from one second to six hundred seconds [ten minutes].

2. Label text
The text that will appear in each label, default is "label".

3. Prepend numbers to label text [0=no 1=yes]
Default is yes, so your labels would sequentially be "0label 1label..." and so on, using the default text.

4. Final label [0=exclude 1=include]
For example, if your selection is sixty seconds long, and your label interval is ten seconds, the final label would be at the exact end of your selection. By default, the above variable is to exclude [not set] the final label.

5. Final audio segment duration equal with others [0=no 1=yes]
Your label interval setting may result in the final segment of audio being unequal with the preceding ones. By default, the above variable is set to make the final audio segment equal in duration with the preceding ones. This might make the label interval
slightly different from your chosen one, depending on the size of the final audio segment.

Note

People using a screen reader can view the label track in Audacity 1.3.3 beta by opening the track menu [alt+t] and clicking on 'edit labels'. The labels and their time positions can be read by cursoring up and down and left-right. press alt+f4 to return to the
main Audacity screen. 

Requirements:

· Audacity