Yes its possible.
For slides 1,2 and 3, insert audio to each slides using
Insert>Movies and Sounds>Sound from file menu. So when these slides appears it will play its own music you put in those files.
For slides 4 to 7, follow the same procedure of inserting audio as above in slide 4. Goto
Slideshow>Custom Animation to show the Custom Animation panel on right.
See the uploaded file
Select your sound icon(triangle like). Then goto its dropdown menu and select
Effect Options. In the new window that will come up, under
Effect tab, click on the radio option that says 'Stop playing
after .. slides'. Enter value 7 there.
It will definately work!