Am i doing this right?

if time out works for her then -yeah, sounds fine

Time out is good,but don't try explaining anything. You just say no hitting and sit her down

Keep your explanations very short at that age. "We don't hit." "Furniture is for sitting on."

That sounds like a great approach. Yelling only makes them upset, and usually it only makes the situation worse. Time out isn't too strict for that age. We do that for our 14 month old, when he slaps me, I say "No we don't hit" and he gets put in his crib for a few minutes. It calms him down and when I go get him and he is attitude is much better.

Get your husband on board with this too. You need to have a unified approach to handling these situations. Stay calm and matter of fact. Good job, mom!

Also wanted to say that if time out works for her it will become a great tool for you. The child I care for hates time outs and it only needs to be mentioned for him to comply with my request. He is very well behaved and it is rare I need ask him if he wants a time out, but he hates it.. Mention the words "time out" when you do it so she comes to know the words and then when you mention it as she gets older she knows the term. Eventually, as she gets a little older, you should be able to ask "do you need a time out?" or "if you want to do that you will have a time out".

I think you are probably "doing" time out right. Time out is a punishment and you may want to reconsider that strategy for her behaviors at this age. You may be able to effectively redirect her & engage her cooperation without assuming that it requires negativity or punishment at all.
If you don't want her to stand on the furniture for whatever reason (to keep upholstered furniture nice, to avoid falls from precarious places that are high or over hard surfaces, so that she learns a standard & doesn't do certain things, etc.) you could respond to her in a way that shows understanding for the fun/challenge she's seeking (in other words, a way that recognizes her "goal" in the behavior) & then redirect her to another way of doing that. Engage her in something you consider appropriate or acceptable that meets the same need.
The approach would be to respond to the total situation, not just the behavior. Why did she slap? Respond.

If your focus is on punishing in order to stop the behavior, you are missing the piece of guiding her toward what TO do at those times. When you recognize the context for the behavior, you are more able to respond to the total situation, which models positive alternatives of behavior (rather than focusing on forcing behaviors to stop.) I see it as: at 17 months, you have an opportunity to build connection rather than create frustration in her with your responses.
With the hitting, that would translate to stopping or preventing the behavior when it happens (if necessary--a single slap you just respond to, but if she's winding up to do it again & again, you prevent those subsequent slaps), and responding to the situation as a whole by recognizing the feelings that drove it. If she was obviously annoyed or upset about something you just did, you verbalize those (you're modeling.) If it was playful, you show her how she CAN play.

keep it short