Eu e a minha colega concordamos uma com a outra sobre o novo horário.

Yes. Both are correct.

• Eu e a minha colega is very common in everyday speech.
• A minha colega e eu can sound a bit more careful or formal to some speakers.

In either case, the subject is we, so the verb stays concordamos.

In European Portuguese, possessives are very often used with the definite article:

• o meu amigo
• a minha colega
• os meus pais

So a minha colega is the normal European Portuguese pattern.
Leaving out the article is much less typical in Portugal, though it can happen in some special contexts.

Because the subject is eu + a minha colega, which equals we.

So the verb concordar must be in the 1st person plural:

• eu concordo
• tu concordas
• nós concordamos

That is why the sentence uses concordamos.

Here it is present tense in European Portuguese.

A useful spelling point:

• concordamos = we agree
• concordámos = we agreed

In Portugal, the acute accent in -ámos helps distinguish the past from the present.

It means with each other or more literally one with the other.

It is a reciprocal expression. It shows that the agreement is mutual between the two people mentioned.

So:

• concordamos sobre o novo horário = we agree about the new schedule
• concordamos uma com a outra sobre o novo horário = we agree with each other about the new schedule

Adding uma com a outra gives extra emphasis to the idea of mutual agreement.

Because the sentence is referring to two females.

• a minha colega is feminine
• uma ... a outra is the feminine form

So this wording implies that the speaker is also female.

Compare:

• two women: uma com a outra
• two men: um com o outro

In mixed-gender situations, the wording can vary, but masculine forms are often used as the default.

Because sobre introduces the topic being discussed: about the new schedule.

With concordar, different prepositions can appear depending on what follows:

• concordar com alguém = to agree with someone
• concordar sobre algo = to agree about something
• concordar em fazer algo = to agree to do something

In this sentence, the relationship between the two people is already shown by uma com a outra, so sobre introduces the subject they agree on.

It is grammatical and clear, but it sounds a little explicit because of uma com a outra.

A native speaker might also say:

• Eu e a minha colega concordamos sobre o novo horário.
• Eu e a minha colega concordamos quanto ao novo horário.
• Eu e a minha colega estamos de acordo quanto ao novo horário.

So the original sentence is fine, but uma com a outra adds emphasis rather than being strictly necessary.

Portuguese often drops subject pronouns, yes, but here eu is part of the full compound subject eu e a minha colega.

So there are two possibilities:

• mention both people: Eu e a minha colega concordamos...
• leave the subject out entirely if context is clear: Concordamos sobre o novo horário.

What you normally would not do is keep only part of the subject in a way that changes the meaning.

Here horário means schedule, timetable, or set of working/study hours, depending on context.

In European Portuguese, horário is commonly used for things like:

• a work schedule
• a class timetable
• opening hours
• a shift pattern

So o novo horário means the new schedule/timetable.