How to do the performance evaluation in terms of secs or minutes? what is the command to use in solidity?
You should not evaluate performance in time units. Your code will not even start computing immediately anyway so whether the actual execution takes 1 or 10 seconds doesn't make much difference.
What you should be interested in is how much gas your code execution takes as gas is the performance counter in Ethereum. You can read more about gas here: What is meant by the term "gas"?
So even if you optimize your code so that it runs 10 times faster but costs 2 times more gas, your optimization has failed.