Vyxal, 13 bytes

ƛ¦Þǔ;∑¦Ḣ:G/*⌈

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Straightforward port of my Jelly answer, go see that explanation for a better idea of how it works. Jelly has some nicer builtins.

ƛ   ;         # Map each task to...
 ¦            # Cumulative sums (instants where a step will complete)
  Þǔ          # Untruth (a boolean list with 1s at those indices)
     ∑        # Reduce the whole thing by addition
      ¦Ḣ      # Get cumulative sums and remove the leading zero
        :G/   # Divide by the maximum
           *  # Multiply by the input
            ⌈ # Get the ceiling