You can't over-charge a battery if you run a small current through it. When the battery is fully charged the resistance of the electrolyte increases and it becomes too much for the small current to flow across it. It's how those battery conditioners that are designed to be plugged in permanently, while the vehicle is stored, work.
If you have a charger with an amp reader, you'll see that the current rate drops as the battery becomes more charged.
Use 2 or 3 Amps and the beast won't ever brew up.. though for a completely flat 65 amp-hour battery you would be looking at 20 hours to fully re-charge it.
A typical flat battery still has plenty of juice in it, so 8 hours (overnight) should be fine.
You can use a higher rate to give your flat battery a quick boost but 5 or 6 amps should be the max and don't run it like that for very long or you'll heat up the plates too much which may cause them to warp, touch each other, internally short-circuit the cells and lead to an early battery death. A slow charge at the lowest ampage that your charger will support is the best way...
Before you charge it, top up the electrolyte to the "Max" mark with distilled water, since that keeps the cells cool (especially if the level dropped and exposed the tops of the plates) and if you add water after the charge, you're diluting the electrolyte and making the battery marginally less charged.