I would add it to the bucket but pour it shallowly on so it is sort of mostly floating on top. Then after 1/2 to 1 hour, I would stir it in. That lets it acclimatize.
You are going to be fine.
If this happens to you ever again, please try pouring your must from one bucket into another, then back again 3 or 4 times before you sprinkle yeast on top. That will add oxygen and eliminate SO2 if it is too highly concentrated.
homewinery products are excellent, IMHO. I have used them and been pleased. But I think they do add some SO2 to the juice to keep it stable. If you also added max SO2, for example, that could tip the scales and make it hard for yeast to get started.
Another thing to watch is the LIQUID temp (not the air). If you are on the low end of your yeast's range, you will have to warm it up to get things moving. A plain ol' heating pad under the bucket or strapped to its side can do that for you. You can remove it once fermentation is underway.
Glad you are sizzling along.