In order to create tension in your audience, you will want to establish a limit to the story. This limit will indicate to the audience what will bring the story to a moment of truth, either running out of time or running out of options. If you want tension to increase as your characters run out of time, choose Timelock. If you want tension to increase as your characters run out of options, then choose Optionlock.
Every argument must come to an end or no point can be made. The same is true for stories. For an author to explore an issue, a limit to the scope of the argument must be established.
To establish how much ground the argument will cover, authors limit the story by length or by size. Timelocks create an argument in which "anything goes" within the allotted time constraints. Optionlocks create an argument that will extend as long as necessary to provide that every specified issue is addressed.
By selecting the kind of limit at work in your story, you lock down either the duration of the argument (Timelock), or the ground covered (Optionlock).
For example, in the film 48 Hours more time would indeed change the nature of burned-out cop Cates' efforts to track down a serial killer. If he had enough time for a leisurely search on his own, Cates (played by Nick Nolte) might not need to "borrow" fast-talking convict Reggie (Eddie Murphy) from jail. Thus the story contains a Timelock, stated clearly in its title, to propel the non-stop action along.
In Midnight Run, however, bounty hunter Jack Walsh's "easy job" of flying bail-jumping accountant Jonathan Mardukas (played by Charles Grodin) from NYC to LA becomes a logistical nightmare as his options become increasingly limited. Walsh (Robert De Niro) tries every available means of transporting Mardukas to LA, but Mardukas nixes each one for good reason. More delays are caused, allowing the mobsters, FBI agents and rival bounty hunters on their tail to catch up as the chase intensifies. If a Timelock were at work here, Walsh would ignore Mardukas' professed fear of flying at the start and force him to stay on the first plane to LA, arriving before the deadline runs out... but that would be another story.