I

It does mean almost the same thing as “à” but the nuance entails that with most verbs the two are not interchangeable; in the TLFi, the following explanation is given;

C. P. ext. [Marque seulement l’idée de repérage]
3. [Dans le temps]

• Partir pour Pâques.

• Pour la première fois le préfet, qui jusque-là avait été humble jusqu’à la servilité, voulut prendre un ton ferme .

• Dieu, quelle belle robe elle pourrait étrenner pour la Saint-Maurice!

When “pour” is the preposition it’s not possible to use any.

1/ The verbs indicating an action that can be considered as happening at one point in time can’t be used;

not “pour”

• Venez à sept heures s’il vous plait.
• Dites-le lui à sept heures.
• Lisez cette annonce à sept heures.

2/ When the action involves a substantial period of time “pour” can be used and it means that the action has to be finished by the time formulated, this time being, so to speak, a deadline, but it doesn’t necessarily have to be so; in certain cases the context calls instead for deadlines that coincides with the end, as in the case of hot meals for instance: the end of the preparation of those has to be the time when they are eaten, in most cases.; that, however is not taken into account by the semantics and the reader is left to his own devices for a more thoutough understanding (his experience of life, let’s say).

• Préparez cette liste de dossiers pour sept heures. (not “à”)
• Elle avait activé les secrétaires pour que le travail soit fait pour l’arrivée du ministre. (In the present case “à” is also possible but can be ambiguous.)
• Partir pour Pâques. (same thing as “à” in this case)

“Pour” is found to specify point-time (specially hours), although this particular piece of information does not seem to be available in the dictionaries.This ngram shows that.

“Pour” is correct in your sentence but “à” is too. That is so because “to be” is not a verb of action.
When applying this principle, it must be remembered that “à” is proper for time given in term of hours but not for other spécifications of time; “en” will be the preposition; so, if you think that according to this principle you can say indifferently

• “Il a demandé que le livre soit prêt pour 2019.” or

• “Il a demandé que le livre soit prêt à 2019.
  you’re making a mistake, as “en” is the preposition for years, months and seasons (except spring).

• Nous avons demandé que la livre soit prêt pour le printemps. or
  -Nous avons demandé que le livre soit prêt au (à le) printemps. (exception for “printemps”, not “en”)

II

There are two possibilities, according to the context.

a) “pour” means “in what concerns“. “Pour ce qui est de” is here synonymous. “quant à” by itself will not do; a complement is necessary: quant au cas de mon frère, quant à l’histoire de mon frère, quant à l’incident concernant mon frère, …
b) “pour” means “from the point of view of“.”Pour ce qui est de” can’t be used, however numerous alternative forms can;

• Du point de vue de mon frère en revanche …
• Selon ce qu’en pense mon frère en revanche …
• Tel que mon frère conçoit les choses en revanche …

In my mind these two formulations

• ” prêt à 19h30″ means ” at 19h30, but not before”

• ” prêt pour 19h30 ” means ” at 19h30, not after”.

These are two ways of considering the same moment (19h30) either as a minimum or as a maximum.

” pour 19h30 ” does not exclude the possiblity to eat sooner. ” Pour” establishes a “deadline”.

“Pour mon frère” means ” regarding my brother.

“Pour” is reminiscent of the latin preposition ” pro”

• In the first sentence, ” pro” : in front of

• In the second : idea of relation