I Have Poison Ivy And Was Prescribed A Methylprednisolone Dose

I have poison ivy and was prescribed a methylprednisolone dose pack (4mg). I was unable to get the prescription until this evening and since this has different amounts on pills at different times and is a taper down med, I don't know whether there is any way to start the pills this evening, or do I need to wait until tomorrow morning to follow the prescribed time and dose.