Well, is something strange
The file have:

100303-0900
100303-1015
100303-1400
100303-1430

If I do:

QMessageBox::information(this, "resultado",lineaHora.right(6))

Gives me -1400

QMessageBox::information(this, "resultado",lineaHora.right(5))

Gives me 1400 when I think that if would give me: "-1400"

Many thanks and sorry for my english!