Not as long as you'd think. Few weeks, maybe more. We already had a 24 pack in the house before all this, I grabbed another middle of last week before the run began. Wife got a 12 pack the same day without knowing I'd already stocked up. So now we have about 60 rolls, but we definitely weren't hoarding. The shelves were still full when we bought it.
In our case, it wasn't panic buying. I wanted to have enough food, bottled water, medicines, and other essentials (like TP) to self-quarantine us for 3-5 weeks if necessary. We do now, and won't be buying anything else for about a month.