For how much time in a day i should put my baby is a walker?

If your intention to introduce baby walker is to let baby to learn to walk, I advise not to do so. This is because baby will learn how to walk themselves and no need any extra assistance for this major development. One day you will find your baby pull up himself by holding on something and start to explore how to walk himself. Any interference will detriment their ability to learn. If your intention is to place a baby in a safe place while you need to attend to other things e.g. housework, you can actually get a playpen/playard to confine your baby in a safe place for a while. For me, I choose to use exersaucer to entertain my baby for a while and make sure he/she is safe while I need to attend to other stuff. I will not let baby sit inside for more than 30minutes.