FSEconomy restricts pilots to logging 30 "virtual hours" during any rolling 48 "real world hour" period. A "virtual hour" is whatever time has passed in your simulator while conducting a flight. If you use time compression to speed up a flight, you may consume 2 virtual hours for every real world hour spent at your computer. In an extreme case of 16x Time Compression, you would fly 16 virtual hours for each real world hour spent at that simulation rate. The inverse is also true - if you slow down your simulation rate to 1/2 speed, you will need to fly for 2 real world hours in order to log 1 virtual hour.
All FSE flight logs, rental payment calculations, etc, are based on virtual time. If you use your simulator for 15 real-world minutes to fly from Point A to Point B at a 4x time compression rate, you will have logged a 1 hour flight and you will have paid a rental rate for 1 hour. The aircraft's log book will reflect 1 hour of time, despite only having used your simulator for 15 minutes.
The 48 hour "window" is a rolling clock. There is no start and end time to this 48 hour period. The virtual time is logged at each landing based on what your simulator reports for "flight time". Each of these logged flight times is added up to determine a total virtual flight time, but only the logs within the past 48 real world hours are added together.
If, at any time, the total amount of virtual hours is equal to, or greater than, 30.0, the FSE System will prohibit you from starting a flight.
Example: You have not flown in several days, so you are starting with a fresh slate of zero hours. If you log a 1 virtual hour flight at 2pm on Monday, you have consumed 1 of your 30 available hours. If you then log a 2 hour flight at 2:30pm on the same Monday, you will have consumed a total of 3 virtual hours, but only 30 minutes of real world time has elapsed between these two flight. At 2pm on Wednesday (48 hours later), that first hour drops off from your record, and you will now only have 2 virtual hours showing within the past 48 hours. At 2:30pm, the next 2 virtual hours that were logged 48 hours prior drop off from your record. You are now back to "zero hours logged in the past 48 hours".
It is probably not possible to keep track of this on your own. The FSE Game World will display your current "hours flown" in the upper right corner of the web page.
If you click on the blue "Hours Flown" figure (seen as 13.95 in the below screenshot), you will be presented with a table of your recently flown flights and when they will fall off the 48 hour clock.
The debate over allowing time compression or not has been a hot topic since the beginning of FSE. Some members prefer very realistic flying and do not like time compression. Others have limited real world time and can only complete a few flights each week. And still others have unlimited real world time on their hands and can fly dozens of flights per day, day in and day out. Each of these points of view has valid arguments for and against the "fairness" of time compression in a game environment in which the actions of all players impact the actions of all other players.
Eliminating time compression completely was detrimental to those pilots who only have an hour on any given day for their hobby. Allowing unlimited time compression for those who can spend several hours a day at their computer is also detrimental to the game if they are able to amass hundreds of virtual hours (and the income that goes with it) each day
The "balance" is that time compression is allowed up to a maximum rate of 16x, but that virtual hours are limited. In theory, the player with 1 real world hour per day can fly approximately the same number of virtual hours as the player with unlimited real world time.