Your Link does not work.
To cut your 4x6"square would probably take about 10-15 minutes in MDF using several passes, or about 15-20 minutes in solid wood with 3 passes. There are a few variables involved such as speed of machine, bit size, depth of each pass.
Do not know about the EBAY machines, but why not buy factory direct from Taney at Jinan quick CNC Router Co? I have a K6100A ( 600mm x 1000mm ) machine. It is a little ripper!