How to compare time in c++ hh:mm:ss.ms string s1 = "04:08:36.095" string s2 = "04:11:18.303"*

#include<bits/stdc++.h>
using namespace std;
int main()
{
        string s1 = "04:08:36.095";
        string s2 = "04:11:18.303";
        return 0;
} 

How to compare s1 and s2 time if they are in hh:mm:ss.ms format