Este horario no me encaja mañana por la tarde.

Here encajar is not literal. Literally, encajar can mean things like to fit into place or to slot in. In this sentence, it means:

• to suit me
• to work for me
• to fit my plans/schedule

So Este horario no me encaja means something like This time/schedule doesn’t work for me.

It is a very natural expression in Spanish, especially in everyday conversation.

The me means to me / for me.

Spanish often uses an indirect object pronoun with verbs like this to show who is affected:

• Me encaja = It suits me / It works for me
• Te encaja = It suits you
• Le encaja = It suits him/her/you (formal)

So:

• Este horario no me encaja = This schedule/time doesn’t work for me

Even though English does not always use to me, Spanish normally does here.

In Spanish, no normally goes before the verb, and object pronouns usually go before the conjugated verb too.

So the order is:

• no + pronoun + verb
• no me encaja

Examples:

• No me gusta = I don’t like it
• No te viene bien = It doesn’t suit you
• No le conviene = It’s not convenient for him/her

So me no encaja is incorrect.

Horario can mean several related things, depending on context:

• schedule
• timetable
• hours
• sometimes a proposed time arrangement

In this sentence, it probably means something like:

• this schedule
• this timing
• this time slot
• this arrangement of times

If someone is discussing appointments, work shifts, lessons, or availability, horario can sound broader than just one clock time. It often refers to the time arrangement rather than a single moment.

Este means this, while ese means that.

Spanish distinguishes distance more clearly:

• este = this, near the speaker
• ese = that, near the listener or less close
• aquel = that over there, farther away

In real conversation, the choice often depends on how the speaker sees the situation, not only physical distance. Este horario suggests this schedule we’re looking at / this option here.

If you said ese horario, it would feel more like that schedule.

In Spanish, the normal expression is:

• por la mañana = in the morning
• por la tarde = in the afternoon
• por la noche = at night / in the evening

So mañana por la tarde means tomorrow afternoon.

Saying mañana tarde is not standard in this meaning. Spanish needs the phrase por la tarde.

Here mañana means tomorrow.

Spanish mañana can mean:

• tomorrow
• morning

But the rest of the sentence makes it clear:

• mañana por la tarde = tomorrow in the afternoon

It cannot mean morning in the afternoon, so here it clearly means tomorrow.

Spanish often uses the present tense to talk about the near future, especially when the time is already clear from the sentence.

Here, mañana por la tarde already tells you the time is in the future, so encaja is perfectly natural.

Compare:

• Mañana trabajo = I’m working tomorrow
• El jueves no me viene bien = Thursday doesn’t work for me
• Este horario no me encaja mañana por la tarde = This schedule doesn’t work for me tomorrow afternoon

English does this too sometimes: Tomorrow afternoon doesn’t work for me.

Yes, encajar is natural, but there are other common options.

Very natural alternatives include:

• Este horario no me viene bien mañana por la tarde.
  • This schedule/time doesn’t suit me tomorrow afternoon.
• Este horario no me va bien mañana por la tarde.
  • This time doesn’t work well for me tomorrow afternoon.
• Mañana por la tarde no puedo con este horario.
  • less direct equivalent depending on context
• Este horario no me conviene mañana por la tarde.
  • more like is not convenient for me

In Spain, me viene bien / no me viene bien is especially common in everyday speech.

Yes. Spanish word order is flexible, especially for time expressions.

All of these are possible:

• Este horario no me encaja mañana por la tarde.
• Mañana por la tarde, este horario no me encaja.
• Este horario, mañana por la tarde, no me encaja.

The most neutral version is probably the original one, or:

• Mañana por la tarde no me encaja este horario.

Different orders can slightly change emphasis, but the basic meaning stays the same.

Because Spanish usually does not need a preposition before many time expressions like this.

Examples:

• Voy mañana = I’m going tomorrow
• Trabajo el lunes = I work on Monday
• Nos vemos por la tarde = See you in the afternoon
• No me encaja mañana por la tarde = It doesn’t work for me tomorrow afternoon

English often uses on / in / at, but Spanish frequently uses no preposition at all.

Yes, it is natural, but depending on the situation, some speakers might choose a slightly more common everyday phrasing such as:

• Este horario no me viene bien mañana por la tarde.
• Mañana por la tarde este horario no me va bien.
• Ese horario no me va bien mañana por la tarde.

Your original sentence is still good and understandable. Encajar sounds a bit like fit in with my availability/plans, which works very well in this context.

You change the indirect object pronoun:

• Este horario no te encaja mañana por la tarde.
  • This schedule doesn’t work for you tomorrow afternoon.
• Este horario no le encaja mañana por la tarde.
  • This schedule doesn’t work for him/her/you (formal) tomorrow afternoon.
• Este horario no nos encaja mañana por la tarde.
  • This schedule doesn’t work for us tomorrow afternoon.
• Este horario no os encaja mañana por la tarde.
  • This schedule doesn’t work for you all tomorrow afternoon (common in Spain)
• Este horario no les encaja mañana por la tarde.
  • This schedule doesn’t work for them/you all (formal) tomorrow afternoon

So the verb stays encaja because este horario is singular; what changes is the pronoun showing who it suits or doesn’t suit.