Originally Posted by
flyme2
All trains to London leave from the Gatwick South Terminal location...
I'm sure you posted with good intentions, but apart from this first statement, the rest of the post is inaccurate or just incorrect.
The ticket machines sell most common tickets, but they may not always sell the best value ticket, and often they invite you to purchase a more expensive ticket when a cheaper one, which is hard or impossible to find, is also valid.
In many cases, an Oyster or contactless bank card will be the best value. For these, off-peak and peak times are simply based on the time you touch in at the ticket barriers of the origin station. If you touch in between 0634-0928 and 1604-1858 on working days, you will be charged the peak fare.
There are no off-peak paper one-way tickets. There is no afternoon peak period for paper tickets on this route.
Off-peak paper return tickets are valid for any train that arrives at a London Terminals station after 0950. Off-peak paper travelcards are generally valid from the 0933 departure to London Bridge. These tickets can be used to enter stations until 0430 the next morning. There may be some obscure tickets with different restrictions.
Your prices are out of date by several years.
A one-day travelcard does not allow unlimited travel between Gatwick and London. It allows one return trip from the origin to the destination and unlimited travel within London zones 1-6.
A typical weekday's daytime schedule includes are 4 Gatwick Express-branded trains and 5 Southern-branded trains every hour to Victoria. There are also 4 Thameslink-branded trains per hour to London Bridge, and 2 to 4 Thameslink-branded trains per hour to Blackfriars/Farringdon/St Pancras and onwards.