Place in oven for the amount of time listed on the box for the type of pan you’re using. I went with the 9x9 recommendation for mine and put it in for 27 minutes which ended up a little gooey in the middle so closer to 30 minutes would have been better.
The red velvet amounts needed will vary based on what kind used. The kind I used had red dye already in it and was more potent than the previous one I had been using so I needed to use less and didn't need any red dye