Split the Overlap
If it really comes down to doing it the old fashioned way, a cam is timed correctly when the valve overlap between intake valve closing and exhaust valve opening is at exactly top dead center. This is true for just about any four stroke piston engine most of us will encounter. There are a very very few exotic racing engines the are not timed like this. The caveat here is you need the valve lifters pumped up to be accurate, so it's tough to get it right on say, a newly overhauled engine. If it's been running recently, shouldn't be a problem. In my long ago misspent youth, a friend had a Lycoming on a newly-bought Super Cub that just didn't develop the power it should have. It ran fine, smooth and all that, but just didn't turn up. We checked the timing as above, found it was wrong, pulled the accessory housing, unbolted the cam gear, moved it one tooth (we could see the marks clearly), put everything back together and it was perfect. Go figure.