A lot depends on the quantities you need to make.
For small-scale stuff the fastest method I came up with was as follows.
It involves a hob a kettle and large pan. It's not quite 2:1 but the bees don't care and the sugar dissolves quicker.
Basically, hob on and kettle filled to 1.8 litres. As soon as boils add into the pan, stick on the hob. Refill (using hot water from the hot tap) and switch kettle back on.
Add 5kg sugar to boiling water on hob and stir. As soon as kettle boils add next 1.8 litres, stir 30seconds job done (at same time get kettle refilled with hot water and back on ready to start next batch). Don't wait for sugar solution to go totally clear, the few undissolved crystals will go into solution when in containers.
Pour into containers (probably the slowest bit), add a few mls thymol solution and job done. Repeat ad nauseum...