i do many, many assignments for ipsos...about 60 +/- per month and i don't know what their payment schedule is. what i do know is that they pay regularly and i have never, ever had any kind of payment issue with them.
actually, i did have a very brief issue with them being a few days late about a year ago due to some kind of computer malfunction but it was rectified quickly with mea culpas issued to everyone who was affected.
they are the poster child for prompt payment along with others such as mf, seelevelhx,north fork, ts, s2n, bestmark, tss, montery and a few others.