You can invest as long as you wish. There is no barrier on duration of investment in this fund or any other fund. This is an open ended fund and after one year of investment redemption is tax-free.
I have myself invested in this fund and this fund constitutes 1/3 or my investments.
Sadly this time they have declared very small dividend - Rs. 1 per unit. But I think in the long run this would prove to be a stable fund.