Learn German: Wir planen ein Treffen für Donnerstag. - We are planning a meeting for Thursday.

While you could say am Donnerstag (on Thursday), using für Donnerstag (for Thursday) specifically marks the target day the meeting is scheduled for. It works just like English: we are planning a meeting for Thursday. Remember that the preposition für always takes the accusative case!

Does für Donnerstag count as a span of time?

Not exactly in this sentence! While your current lesson covers spans of time, für can also be used to set a future target date or deadline, as it does here. If you wanted a true span of time, you would say something like für drei Tage (for three days).

Why is Treffen capitalized if treffen is a verb?

Here, ein Treffen is a neuter noun meaning a meeting or gathering. In German, you can often turn an infinitive verb into a noun simply by capitalizing it. Because it is the direct object of what we are planning, it is in the accusative case.

How do we know it means are planning and not just plan?

German does not have a separate continuous tense like English does with its -ing verbs. Wir planen can mean either we plan or we are planning depending on the context. Here, the English translation uses are planning because it sounds more natural for an active scheduling process.