The quality of Time is different for everyone. At one instant a business man gains billions and at the same time a poor man even loses his last source of income to earn bread for his family. Similarly many examples can be quoted for contrasting different or opposite things happenings to different people at the same time
So the definition of "Good or Bad Time" depends upon human being himself.
A good Muhurta can be defined as: the best possible starting time of an activity at a particular place for a human being or an entity to obtain his/its desired goals and have all round prosperity, happiness and success.
The moment one starts an activity or engages in action or work, he becomes doer (karta). His actions have definite consequences for that person, the society and the activity itself in short and long term. The over all experience one undergoes depends upon:
His own destiny and hence karmas he indulges in. Consequently he undergoes some experience depending upon the outcome of one's actions (karmas). There are 3 types of Karmas according to Hinduism: Fixed (Drid Karma) which cannot be changed, Not fixed or Variable Karmas (Adrid Karma) they may be changed and Combination of fixed and variable (Drid-Adrid Karma).
Muhrata: starting time of an activity. Just as the natal time governs the entire life experience of the native, the starting time of an important activity is a new birth of the native with respect to that activity.
Muhrata is a great Vedic Remedy as a preventive measure to avoid any undesirable effect and have success and happiness from an undertaking. By choosing to start an activity at an auspicious time one can remove most of the negativity associated with the following two types of karmas : variable karmas ( Adrid Karma: that can be changed) and combination of fixed and variable karmas (Drid-Adrid Karma). These karmas are associated with some definitive compulsions but can also be changed.
The fixed karmas (Drida) are those which one must undergo and experience in this lifetime and cannot be changed. Just like all other karmas they are desirable and undesirable both.
So someone destined to fail in exams will only appear in the exam when the time for his success in exam is really bad. In other words the celestial bodies (constellation, planets etc.) for that person will be badly placed in the Muhurta chart of the exam.
A native destined to rule a nation will file his nomination and consequently take formal responsibility (oath) at a time, very conducive for him to lead the nation.
Spaceship/satellite will crash only if it has started its mission at a particular time, inauspicious for its own survival during the mission.
The quality of Time felt and perceived by a human being is based on 5 general aspects which are called Pancha- Anga or 5 Limbs of Time in Jyotish. If these five aspects are excellent for someone then he is bound to experience good time in his life.
Tithi: feelings, emotions, happiness and relationships of the native.
Vara: health, vitality and energy level of the native.
Nakshatra: longevity of the native or the number of breaths in his life.
Karana: achievements, success, wealth and material well-being of the native.
Yoga: binding element that keeps everything in union for of the native, that gives a meaning or purpose to existence.
A Muhurta can be found for almost every activity. For a Vedic astrologer, finding an auspicious Muhurta, is a challenging job as he has to first understand : what native is looking forward or wants to achieve from the Muhurta and then try to extract the best for him from the heavenly bodies in motion in the sky, considering various constraints from practical situations around.
It is not practical to do every single activity at a good Muhurta but for some important activities that are significant for one's life, should be started at auspicious Muhurta to achieve the desired objectives.
It is recommended to start important activities, which can have significant impact on our life and which require considerable expense , at a suitable Muhurta such as:
Starting a business or an association
Joining a job, starting a work
Entering into a new house
Buying, Selling, Investing