how long will a 12V 5W solar panel take to charge a 12V 1.3Ah `lead acid battery
12VDC is the nominal output voltage but may run as high as 17VDC1.  If you actually achieve 5W output from the panel that would be 0.41A at 12VDC.  Thus the theoretical minimal time to charge is 1.3Ah/0.41A = 3.17h.  In the real world though you'll see losses from the charge circuitry, atmospheric attenuation, sub-optimal orientation, etc.  Realistically, under good conditions you'd probably be looking at a full day or more to charge the battery.

1 https://www.solaronline.com.au/solar_system_basics.html