I don't know what they do in Mexico, but usually we do pray the Basilian liturgy.http://www.copticchurch.net/topics/liturgy/liturgy_of_st_basil.pdf
It's the shortest of the three main liturgies the Coptic Church uses (other than Gregorian and Cyrillian/Mark). If anything, traditionally, at this time in Lent, the Cyrillian liturgy (traditionally attributed by St. Cyril of Alexandria to St. Mark the Apostle) should be used, but I'm not sure if the Church got that far in establishing the Spanish translation of it. Just in case:http://www.copticchurch.net/topics/liturgy/liturgy_of_st_cyril.pdf
Almost every Coptic Church I went to in NJ/NY uses a lot of incense in comparison to EO churches I went to, so brace yourself for a cloud if the priest likes to put extra coal. Morning prayers and raising of incense should take about 30 to 60 minutes, the liturgy of the word about an hour, and the Liturgy of the Eucharist about another hour. So ya, roughly 2.5 to 3 hours. Lots of standing, but if you see a lot of people sitting around you, when some are standing, and you're feeling tired, usually no one bothers you.
Important times to stand:
When the priest is going around the church with the censor
At the prayer for the Holy Gospel and the Gospel reading itself (this Sunday, it will be Temptation Sunday, when the Lord gets tempted in the Mountain).
When the altar servant says "You who are seated stand"
The Institutive Narrative (prayer of turning the bread and wine into Body and Blood)
The Fraction until the end of the Eucharistic distribution
You'll know when a group of people are all of a sudden moved to stand up, when are moved to kneel in worship, when are moved to sit down (usually sitting is only for the sermon and readings, except the Psalm and Gospel).
Certain hymns at Lent are sung differently, some in different tones and words. Lent commemorates the 40 days and nights Christ fasted before ministry. So a lot of the hymns will reiterate that.
Usually I find the people are very kind, and if you get lost following along with a book, a congregant may assist you.
That's all I can think of at the moment.
PS oh ya, and we use cymbols and triangles for instruments, but traditionally was used just to keep the beat of the hymns flowing, that the congregation should follow along with the cymbols. More likely today however, cymbols are just instruments and there's a head deacon that carries a microphone that usually carries the flow and beat of the hymns, and the cymbols are forced to follow along with him.