Star Trek Timelines utilizes a variety of special offers, which might be presented to you in a variety of ways. Some are more predictable than others, and it's helpful to know which ones you can expect and which ones might be more elusive.
Firstly, it's important to note that any and all special offer trends are subject to change at any time. An offer that we've previously run is not obligated to run again in the same fashion or at all. We're always working to find the best spectrum of value for all types of players, and that means experimentation and iteration.
Currently, offers centered around Event-related content are common and widely-available. You can usually find several offers of varying price-points over the course of an Event that include featured Crew and other useful resources to help you get ahead. These and other globally-available offers usually appear in the Time Portal.
Some offers are available to everyone on an individual basis when certain conditions are met, but they won't always trigger, so it's important to jump on them when they do present themselves as you never know when the next one will appear. For example, you might find that enlisting a particularly high-ranking Crew member also invites an opportunity to improve their effectiveness.
Finally, some offers appear completely sporadically, and not to every player in the same time frame. It is likely that you may see some of these offers over the course of your tenure as a Captain, but you can never count on them. When that time comes, be prepared to leverage the opportunity!