This is just a personal observation. 

I currently have 2 infusion options open to me by my doctors, a 3rd if I end up in an ER (no thanks). 

I have often "waited" until things got so bad that I was having trouble getting any treatments let alone infusions to provide even a 24 hour break from the pain. 

When they are really bad my doctor prefers giving me methylprednisone as an infusion.  I am often reluctant with this due to the nasty side effects I experience including a secondary headache.  I last had one in November.  At my follow-up visit I let them know I wouldn't wait so long next time. 

About two weeks ago "next time" came.  It started just before one of our snowstorms hit (always a weekend) and I called late on Monday, so just about 48 hours in.  My doctor had also recommended I call when they have lasted about 48 hours.  On Tuesday they made arrangements and offered me the magnesium option.  I had almost written magnesium off as ineffective for me.  I decided to take it because I don't usually experience any side effects, with the agreement that if I didn't get relief I would come in the following day. 

So far, the magnesium seems to be holding.  I have had a few migraines in the past two weeks, but they seem to last less than 12-16 hours. 

The key is that it pays not to wait when it comes to getting an infusion.  The sooner it's caught, the easier the treatment. 

I had been asked by someone on my doctor's staff (not familiar with me) why if it was so bad that I didn't just go to the ER.  I tried to explain that they wouldn't contact my doc and would only get what the ERs in this area offer(benadryl/compazine), which is incapacitating and ineffective. 

So, I am quite pleased and plan to continue to not wait until things get so bad. 

I continue to wait for insurance approval on the botox.  Something about them needing to use my insurance's supplier.