To be safe for your eyes (if you are going to look through the viewfinder to frame and focus) then the filter MUST block 99.997% of the Sun's energy both in visible wavelengths as well as in the infrared wavelengths. That's an absolute minimum.
However, most certified solar filters are blocking 99.999% (ND 5.0) which works out to about 16.67 photographic stops. Basically one photon out of every 100,000 can make it through the filter (e.g. that's what the Thousand Oaks solar filters and Baader solar filters are blocking.)
You may remove the filter no sooner than 50 seconds before totality and probably want to make sure it is removed at least 20 seconds before totality.
HOWEVER... DO NOT look through the camera to do a final adjustment to frame and focus once that filter is no longer on the camera. Do your final frame & focus before removing the filter.
If your camera isn't on a tracking mount, then while the filter is still on the camera, compose the sun & moon to about the left third of the image (it will appear to move from left to right). Earth spins at about 15 arc-seconds per second... so in 4 seconds that's 1 arc-minute. In 120 seconds, the sun will basically move the equivalent of it's own diameter. The eclipse will last around 2 minutes and 38 seconds at max ... most people will experience at least 2 to 2.5 minutes. (so that's 150 seconds). But since you want to remove that solar filter about 30 seconds before totality... you should count on it taking more like 180 seconds. That means the Sun will move about 1.5 times it's own width (if your camera is not on a tracking mount). That's why I suggest composing the sun a little to the left... so that as totality is happening it will be just about in the middle ... and will be slightly to the right as totality ends.
If you do have a tracking head (such as a tracking telescope mount or a photo tracker like the Sky Watcher "Star Adventurer" head or the iOptron "SkyTracker Pro" head) then you can just center the sun, set the tracker to the Solar rate, and let it go.... it'll keep the sun in the middle the entire time with no drift.