Hey Gary,
I was first (mis)diagnosed with a stroke so this is a question I asked. A stroke happens in an instant. One moment you are feeilng like you. For us that is our normal baseline. And the next moment, you have having significant symptoms.
I know a guy that was talking one moment, then the next couldn't talk. It is not at all gradual. When this gets tricky is when you wake up with new and significant symptoms. You have slept through the gradual part. I once woke up numb from the mid shins down......it was the beginning of a flare.
It can be hard to know......if you suspect a stroke at all, then it is a 911 medical emergency. Better safe than sorry. You can make sure you are not at risk for a stroke as well. You need to monitor and maintain decent blood pressure. You need to know what your cholesterol is and know your family history. If you have any of those worries then assume stroke and get checked out.