Daily Login Rewards is one of many limited time Events in Rise of Mythos. For a set number of days, you will be able to log into the game each day, click on the Events tab, and claim a free item, mount, or currency. Sometimes, incredibly rare items such as a Fire Ruby are included in the event. Free items given through this event are determined by the developers and are the same for everybody who participates.
Like all limited time events, Daily Login Rewards will have a deadline. If you do not claim all the free items given through this event by the deadline, you will not be able to obtain them this way unless the next iteration of this event.