The time from first contact (C1) when the Moon first starts to cover the Sun until fourth contact (C4) when the moon moves off the sun is nearly 3 hours (it will vary slightly depending on where you are and how close you are to the center line.) I get 2 hours 47 minutes when I punch in the location where I plan to observe.
For all but a couple of minutes of this, you won't have totality.
During totality you don't need any filter at all.
For everything else (and this includes 99% eclipsed... when we say "totality" here... we actually mean that the disk of the sun is 100% covered) you'll need the filter.
But this means that filter will be on your lens for more than an hour (closer to 1.5 hours), it will come off for a couple of minutes, and then it will go back on for another roughly 1.5 hours. You won't want to hand-hold that.
The filter needs to be secured to the front of the lens. You have a few options here.
You can buy filters that are sized for your lens. If you wanted to get a thread-on filter, those are available too (Thousand Oaks Optical makes them). But the more popular type are the ones that fit over the front like a cap. Size them so that the inner-diameter of that cap is at least as large as the outer-diameter of the front of your lens. Thousand Oaks usually includes felt strips that adhere to the inside and you use this to create a moderately snug fit. Some models have nylon screws to snug them down (without scratching the lens).
But if you're handy with a craft knife, you can buy a sheet of solar film, get a piece of heavy card-stock, and make your own filter. Find a cardboard tube with a diameter large enough to fit over the front of your lens and use that to build a filter... cutting the solar film to fit. I have a few commercial filters ... but I have a lot of friends in the club who make their own. There's pretty much no difference in terms of the optical quality so as long as a home-made filter fits and works, you'll get the same results.
BTW... these sheets are film are like mylar. When you build your own filter, it WILL have wrinkles in it... don't worry about the wrinkles, they're not going to effect the optical quality (you won't see any evidence of wrinkles in your photos.)
You'll need a solid tripod. The Sun/Moon will keep drifting out of your field of view if you don't have a tracking head ... so you'll want to keep checking the composition and nudging the camera position to keep everything in your frame.
As totality approaches, you'll need to do one last composition, framing, and double-check focus BEFORE you remove that filter. So about a minute before totality, check that the sun/moon are just left of the center of your frame. The sun moves 1/2 of it's diameter every minute... or it's entire diameter in 2 minutes. Since totality lasts (for you) about 2.5 minutes that means the sun will move 1.25 times it's width during that time. But remember... you'll be doing the final composition about a minute before totality starts... so you'd want to position the sun just fractionally more than one full solar diameter left of the center of your frame.
To avoid leaving anything important at home... setup everything at home and simulate the event. If you need a laptop, tethering cable... or if you're using a remote intervalometer, or smartphone software to control your camera, etc. Filters, lenses, teleconverters, etc. Whatever you need, make sure you have everything. Now take everything you just used for your test and make absolutely certain it gets packed for you trip.
I have (twice now actually) traveled hours to do astronomy events and discovered something critical got left behind.
to suit your lens. Have it in place for the partial phases and when Eclipse Orchestrator tells you to take it off, just slide it off and then it slides back on at the end of totality. Simple and safe.
