Schema for storing historical data on shared identifiers
Looking at the data you posted, what would be the expected result from your point of view?
The fact that users share the same desk/IP shouldn't be a problem as long as both users are reported while they're logged in.
You could either use your current table design (a single table with Row_Id, update_time, IP and User) or an aggregated table with Row_Id, IP, User, login_tim, and logout_time.

I'd decide based on the expected number of unchanged logins. For example, if users usually login in the morning and logout in the afternoon, then I'd go for the aggregated version. But if the scenario is more like a user to log in and log out within a short period of time and a high frequeny, then I'd go for the current design since aggragation wouldn't reduce the number of rows significantly.

How many rows do you expect per day (given your current design)?