Answered by Shaykh Faraz Rabbani
Muslims have a reputation of always being late for everything. MST (Muslim Standard Time) is jokingly understood to be a considerable amount of time after the agreed upon start of an event, work, school, or meeting. What’s the fiqh of punctuality and being late?

Wa Alaykum Assalam wa Rahmatullah wa Barakatuhu,
In the Name of Allah, Most Merciful & Compassionate
Agreeing to be somewhere at a given time is like a promise and therefore, the Fiqh of Promises applies to it. Making a promise without firm resolve and reasonable surety of fulfilling it is improper, but not sinful because of secondary issues that may arise and prevent one from fulfilling it.
However, contractual matters such as jobs, classes, appointments, and the like are different. Allah says: “Oh you who believe, fulfill your contracts”. The scholars mention that contracts’ here refers to every form of commitment. It is obligatory (fard) to be on time if this is the expectation. Even being a little late is at least improper, and is unbecoming of a Muslim in our times. Undue delay is otherwise sinful, except for slight delays that are customarily overlooked.
The believer should uphold themselves to the most excellent of character, for the Messenger of Allah (Allah bless him and give him peace) said “The closest of you to me on the Day of Judgement are those best of character”.
Shaykh Muhammad Qaylish mentions that in our times, when the Shariah is distant from society, we are ambassadors of Islam and must act in order to uphold a favourable impression of Islam. This entails:
1) upholding commitments with excellence 2) being easy-going without being lax.
And Allah Most High knows best.
Wassalam,
Faraz Rabbani
[transcribed by Sr. Nosheen Mian, from the SunniPath Academy Live QA for the Essentials of Worship course, 4th December 2004]