Is it healthy to worhout on the abs every day?

No, abs are muscles like any other. You wouldn't train your biceps every day!

They need days off to recover and rebuild. Concentrate on quality rather than quantity, prehaps looking at 5-10 minutes 3 or 4 times a week, focusing on correct technique. Core exercises are very useful, such as the 'plank'.

Make sure your diet is right for you, and you are sleeping well also.

Getting a good sleep pattern is super important, get a regular body clock sorted out and never sleep less than eight hours a night. Recent research has proven that if you get less than six hours sleep you begin to store fat around your mid section much more readily.

As for training you can train your abs as much as you want actually. Its not like every other muscle because there is a much greater pool supply of blood within that region of the body. 30 mins daily would be ideal mixing up reps and isometric exercises like the plank each session. I myself simply cannot train more than four or five times a week because I find the muscles get sore, work within your limits and keep an eye on your progress, Id certainly have a couple of days off training each week.