Another method that I prefer is to put a screwdriver (or something else too big to fall into the cylinder) in the plug hole and observe it moving up and down as you rotate the crankshaft. This makes it easier to determine when you are exactly on TDC, which is important, as you are trying to confirm (or not) a discrepancy of only 5 degrees, so accuracy is essential.

Don't be too concerned about damaging your engine with incorrect timing. You have a knock sensor. If it is working correctly, it will prevent excessive advance, whatever the base setting. If it's not functional (unlikely) you will hear loud pinging, which should alert you to take your foot out of it IMMEDIATELY and figure out the cause. (This is true even if you have no other issues with the timing) In general, with a knock sensor, having the base timing overly retarded is more of a worry. This can overheat the exhaust valves, manifold, turbo etc.