You can estimate how long it takes to charge a battery by taking the capacity, dividing by the rate, and multiplying by 125%.
For example: a 2200mAh battery charging at 500mA? It'll take 2200/500 * 125% = 5.5 Hours. Less if its not fully drained!
The chip in the MicroLipo can charge at up to 500mA rate. To make it safe for all our batteries, we set the default rate to 100mA. It's very easy to update the charge rate, however. On each board, look for the solder jumper that looks like this:
There's a few stages for charging batteries: pre-conditioning, constant-current and then constant-voltage.
Pre-conditioning is when the battery is very low, and requires low current. Constant-voltage is for 'topping up' the battery when its almost completely full. Constant-current is where the bulk of the charging occurs. If your battery is not ready for constant-current or if it is coming out of the CC stage, it will draw less than the max charge rate current!