Is it okay to...?

That doesn't sound healthy. If I am understanding correctly you have set a calorie deficit goal which is probably 500-700 below your maintenance calories and then you are going a further 400-800 below that??? So what are you consuming daily? 800-1000 Cals? That's really low and may impair you body's ability to maintain healthy function on your organs.

Try to hit your target.

Taking a day where you eat back to maintenance or above is a good idea. I believe it staves off plateau and it gives you something to look forward to which makes it easier to stay good during the other 6 days.