I found why time was being further altered. The reason is that slices are pointing to original array. Okay. The problem fixed.

internal/radio/icecast.go

@@ -73,7 +73,9 @@ func IcecastLastPlayedSongs(lastNSongs int, playlistPath string) ([]Song, error)
 			if lastNSongs > lpcLen {
 				lastNSongs = lpcLen
 			}
-			return lastPlayedCache[lpcLen-lastNSongs:], nil
+			var ret []Song = make([]Song, lastNSongs)
+			copy(ret[:], lastPlayedCache[lpcLen-lastNSongs:])
+			return ret, nil
 		}
 	}