I think you can use it as needed too -- I guess it depends on what you're using it for? My first awareness of CBD was that a friend gave it to her son to prevent seizures (which it was entirely effective at for 5+ years) and in that case they needed to keep it in his system at a somewhat constant level. For me, I was interested in sleeping better, so it wasn't an "as needed" situation exactly -- I don't always know when I'll have trouble sleeping. I also wanted it in my system regularly to see how it affected my sleep.

As medications go CBD and marijuana are very safe so I would just experiment, because everyone's system is different! But if your T suggested it as needed then never mind what I said about half life and all that.