In what case to use the next (with the definite article) with time periods that follow the current time period?

Use next without the or a preposition when talking about a time period that follows the current time period. However, when talking about several time periods that follow the current time period (in this example: several weeks), use the next and the respective preposition: e.g. in the next.

For example, a phrase like this: The project will be completed in the next few weeks.
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