Is it the right time for me to invest in the shares of one big public sector bank or whether I have to wait for sometime?

Stock market prediction is very difficult
The price of any share depends upon so many factors.
Fundamentally, it is the perception of the investors about any stocks and not actually the performance of the company. The performance of the company plays a greater role in providing a better image amongst the investors. Even then, sometimes, the investors are forced to believe certain myths, inforamtion, rumours etc., which indirectly affects the value of the share in the market.
You can invest in shares as an active or a passive investor. An active investor, takes part in the activities of the share market every minute or at least every one hour.
The passive investor invests some amount in growth stocks and forgets and after a long time, he finds that the share is up by some points and he sells the share and he is happy that he has gained some profit. He avoids risk
The very active investor buys a share in huge volume by 10.00 A.M. in the morning and goes on watching the movement of share every minute and by 11.00 a.am. he sells the shares at Re. 3/- rupee share profit
I shall cite the following example
You buy ABC company shares - One share at Rs. 2000.00 - Total number of shares purchased - 1000 by 10.00 A.M. and the value of the shares - 2000000.00
You are watching the price movement - it goes up and down and finally at 01.30 P.M. you find that the share is priced at Rs. 2014.00 and your broker says that the price may be the highest for the day. Now you are selling the share through your broker and your selling and buying transactions are squared out.
You gain a profit of Rs. 14000.00 and out of the profit, you pay brokerage for buying and selling transactions - Rs. 3000.00 and your net gain is Rs. 11000.00 for the day and you should remember, that without any investment of any money in the market except by taking some risk and spending time and energy you had gained this profit.
Now this is an answer for your question
You buy the share at any time and after some days, when you feel that you can sell, you immediately sell. Even one rupee gain for a share is a profit for you. There is no ultimatum for upward and downward trends. Have one reliable broker and he will be guiding you in this connection.
Always remember when it comes to share market
BOOK PROFIT.
Just by viewing in the paper that the price of the share is going up will not provide you even a single moment. Buy and sell it at a profit - let the profit be even a single rupee. This is the fundamental principle each investor should know