I have usually only got very faint ones for about 2-3 days each cycle.
Last cycle it started off faint and then work to one with the same colour/ darker than the control, so 2 days faint, then 2 strong days. I say that there were 2 strong days because as i got closer i used 2 different brands- one was ovunow (internet ones) and fortel. Ovunow gave me the line darkest first and fortel the next day.