Learn French: La relecture de la bibliographie sera difficile. - The proofreading of the bibliography will be difficult.

It can mean 'proofreading', 'rereading', or 'copy-editing'. It is simply the prefix re- (meaning 'again') attached to lecture (meaning 'reading'). Because this sentence mentions a bibliographie, 'proofreading' is the most natural English translation in this context.

How could I add 'between now and tonight' to this sentence to practice this lesson's future time limit grammar?

You would use d'ici followed by the time expression: La relecture de la bibliographie sera difficile d'ici ce soir. You can also place d'ici ce soir at the very beginning of the sentence to emphasize the deadline.

If I wanted to add a verb and say 'difficult to finish', would I use à or de after difficile?

You would use à, resulting in sera difficile à terminer. When a specific noun is the subject of the sentence (here, La relecture), French uses the structure Adjective + à + Infinitive. You only use de when starting with the impersonal Il est or C'est (for example: Il sera difficile de terminer la relecture).