This not the case by the RAW - a magus must test to avoid twilight he gains two or more points of warping in a single event which thus requires a double botch - twilight prone reduces this to one.
Which raises the interesting question - can a nonTwilight prone magus voluntarily enter twilight upon taking a single point of warping? After all, the magical impetus is there, it's just not to all-demanding that it must be actively resisted.
Isn't that what we just said? I said a double botch is required. Rex pointed out that Twilight Prone reduces that to one. I don't understand where our error is.
Ahh. Mea culpa. I parsed "Unless the magus is Twilight Prone, then a single botch will suffice." as "Unless a magus is Twilight prone, a single botch is needed" rather than as "if a magus is Twilight Prone then only a single botch is needed."
I'll just go and stand in the corner looking sheepish, shall I?
Thank you very much for your answers