try this other way
1) Open the file
2) From menu "Edit" select command "Define markers manually"
This open a small window containing some box. There you must define start and end of selection. If you want obtain only the first 30 sec of the song, then you must leave all values on the first line at 0 and put a value of 30 in the box "sec" of the bottom line.
3) Verify the selection.
Press the spacebar to hear what you have selected. If 30 sec are not sufficient o are too much, then repeat the step 2 and modify the value on the box "sec". Obviously, if you want retain more of 60 seconds, then you must select 1 on the box named "min", because 60 seconds are 1 minute, and if you want select 65 seconds you must put 1 min and 5 sec, and so on.
4) From menu "edit" select the command "Copy to file"
Hope this help