To express that the event will continue until a specific time in the future the sentence would be rewritten in future perfect progressive tense. Future perfect progressive tense refers to the state of action that will be continuing until a specific time in a future.
Future perfect progressive tense is formed as subject + will+ been + present participle of the verb.
Therefore, the sentence would be rewritten as,
The students will have been painting for an hour without a break to create their Rockwell-inspired art.