I'm still a learner, and correct me if I'm wrong, but i think it should be "a las seis de la mañana". The preposition you could use for time of day is por, for example "I usually stay at home in the morning" - > "Suelo quedarme en casa por la(s) mañana(s) ".

About the pronouns:

You would say "Vale, la espero", you omiss the "llegada" because it has been mentioned in the previous sentence and therefore "la" refers to and substitutes "la llegada". Another way to say it is "Vale, espero tu llegada".

Furthermore, *llegaras" is 2-a persona singular for Pretérito imperfecto de subjuntivo. You would need to say "llegarás" o "llegas", both are fine even if you use present tense since it stands to reason that you refer to the future.