'Starvation Mode' is a term that is widely used to describe a series of events that happen in the body during a prolonged period of calorie deficit. There is lot of debate about whether these events actually exist, however our current understanding is that having too few calories (whether starvation mode actually occurs or not) isn't a healthy way to lose weight.

So to answer your specific questions - the rule of thumb is to think of 1200 calories as the cut off for any sensible calorie restriction. If you are someone who does a lot of exercise and are regularly burning 600-700 calories in an exercise session then it would be advisable to start eating some of your burned calories. It isn't really feasible for a body to stay healthy and recover properly from the exercise if you have less than this amount.

So for example:-

Calorie allowance = 1200kcal, Exercise = 700kcal per day (your net calorie intake would be 500kcal = too low)

Calorie allowance = 1400kcal, Exercise = 300kcal per day (your net calorie intake would be 1100kcal = verging on OK)

So really, it's about understanding your body and how it adapts to exercise because unfortunately, no two people are the same. My advice would be to try and made sure your net calorie intake doesn't fall below 1200kcal on a regular basis. Keep an eye on your weight loss, and ensure that you're not losing weight too rapidly at any point - 1-2lbs per week is about right.

As I said at the beginning of my reply, starvation mode happens usually after a period of prolonged calorie deficit, so in answer to your query, it won't happen on a daily basis. It will take a while ( but will depend on the individual how long) for the body to adapt to a reduced calorie intake so it could be a week or longer before any long term changes in metabolic rate take place. Starvation mode basically means that the body has recognised that there isn't enough nutrition available in the body (either through not enough food, or too much exercise) to survive long term, so it starts to hold onto what nutrients you have (i.e. fat and muscle stores). Metabolic rate may slow down, and some believe that this can be something that is altered for the long term.

So in summary - starvation mode is a 'state' that the body may reach after a period of prolonged calorie deficit. Ensuring your net calorie intake doesn't regularly fall below 1200kcal is a good place to start however this will be very individual, so keep an eye on intake, activity levels and weight loss.