Time of microwaving frozen meals?

When you have one of those frozen meals to heat up in the microwave e.g. Shepard's pie, do you have to heat it up for the time they say? If it says 7 minutes can you microwave it for 5 minutes and it will still be cooked? Are frozen meals already cooked? It's just when I microwave some meals for the time... show more When you have one of those frozen meals to heat up in the microwave e.g. Shepard's pie, do you have to heat it up for the time they say? If it says 7 minutes can you microwave it for 5 minutes and it will still be cooked? Are frozen meals already cooked? It's just when I microwave some meals for the time they say, they are too hot.

Thanks in advance. :)
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