One thing I should mention is that the watering interval for different growers will invariably be different depending upon their particular clonebox conditions.
It has been a little cool here recently, so I just added a small fan to my clonebox to circulate warm air coming off the fluoro ballasts. The fan is a cheapo 100mm desktop fan, fixed in place above the fluoros, blowing air upward, away from the plants. However, the air still bounces off the interior top of the clonebox and makes its way down to the clones.
This fan has sped up the evaporation rate from the cubes dramatically. I checked them yesterday morning to find that 4 clones had wilted.
Thankfully, they didn't totally collapse and were recoverable.
I normally water clones 1x day by dipping only the bottom 1/3 of the cube into the clone watering solution for 2-3 seconds. I've taken to dunking the whole cube now.
Without the thermostatic exhaust fan control (set to 26.5C), the 30C fixed-temp heatmat and now the circ fan which have combined to make for a high evaporation rate in the clonebox, dunking the cubes fully would quickly cause overwatering symptoms.
When setting up a new clonebox, one should wet some cubes, weigh them and run them (without any clones in them) in the clonebox for a few days until you get a good feel for how fast cubes will dry out in your particular conditions. Ideally, you're looking to have about 1/4-1/3 of the water weight remaining after 24 hours. If things dry out too fast but temps are still right, you may have to water more lightly but twice a day.
Keep in mind that once clones have developed a bunch of roots, they will suck up much more water than before they had set root. Check them at least a couple times a day.
If you must 'idle' rooted clones until you have space available for them, you may wish to shut off the heat mat and turn the air thermostat down a few degrees to slow them down a little. Clones work best when 'fresh,' though, and should be planted into growing media after several taproots are showing but before roots are overdeveloped.