Well for my money that's good advice about knowing when to dedicate 100% concentration to which career. As I said - I do know of at least one person who managed to fit in some pretty decent quality music work whilst working towards his commercial pilots licence but he is probably the exception to the rule.
When I started on the ladder for CPL I put a total block on all musical work (much to the annoyance of those muso's who know/knew me!) and opted for the 100% commitment to aviation route. There have been the odd time due to unforseen circumstance (waiting for VISA, delay in getting into ground school brush up course before exams etc) where I've managed to fit some music work in but in doing so have also ran the risk of whetting my appetite for more music so you have to be on your guard and not afraid to say no to pressure to play more.
Music and flying are similar in that they can be addictive to the exclusion of all else and if you're getting phone calls about projects that sound very interesting it can be very frustrating to say no. I have one guy who rings me once a week without fail to try and enrole me into his band! Another more promising contact I have had serious lack of sleep over turning down work for. I will probably live to regret it but flying will very soon be at the fore of my concerns again with exams so cannot take the work as it won't be finished before the hard study comes back into my life again. It is a shame but that's the rub.
VFE.
My post may appear slightly garbled but I hope it makes sense!