For me, modafinil works straight away pretty much, but each dose only lasts for about 4-5 hours. I’ve been on it for 3 years now and it still works (and at the same dose). It does very little for my muscle/motor fatigue, but it keeps me awake & alert and I rarely have to sleep during the day any more. I almost always sleep very well at night too, and I didn’t use to:-)
Working out the best timing and dose to get that effect can be tricky mind you! 200mg at once made me hyper so I take 100mg twice a day. I tried different times and found that 10 and 3 works best for me (I take the second one later if I’m planning on staying up late that evening).
Taking 100mg when my fatigue is OK doesn’t make me feel much different, but if I forget to take it, I get absolutely knackered. It’s a bit like, without modafinil, my body goes on a fatigue nose dive as the day goes on, but with modafinil, my fatigue stays level / doesn’t decline as badly.
I hope you’re lucky with them