It doesn't matter when you take the DAT. You have to apply year ahead of your anticipated graduation year if you want to start dental school right after your undergrad.
I sent my application by the end of May and took the DAT on the first weeks of July. I had the same plan as you have: I wanted to go straight to the dental school right after my graduation. But, I found it really hard and frustrating. Because the dental admission process is a hard and long process and it may interfere with your senior year courses. I don't know what major you are in, but I was biochem and most of the hard main biochemistry classes were concentrated in my senior year including my senior undergrad thesis project. Taking a year off is not going to hurt you, it may increase your chance because you will have a degree when you are applying and you may concentrate on working to earn money to minimize your loan dependence , and finally having been working outside they will count you as a mature student who is ready to face dental school. but, this is your application process and probably you have plans. whatever is your choice good luck with that. Apply early and take the DAT no later than mid-July so the schools would receive your official scores by August.🙂