"Finish work" as early as possible

Jelly, 20 bytes

³œ-;⁴Ṃ;¹S>⁴
ŒPÇÐfS€Ṃ

Try it online!

TIO is fast enough to finish the last test cases within its 60 second time limit, even if just barely.

Background

The algorithm is both simple and inefficient:

1. We generate all subsets of T, counting multiplicities.

2. We filter the the subsets, keeping only those those subsets S that satisfy one of the following criteria:

   • S is different from T, and the sum of the elements of S and the minimal element not in S is larger than L.

   • S and T are identical.

   The filtered T (let's call it T') now contains all lists of task that do just enough work (or even some overtime).

3. Of all S in T', pick the one with the lowest sum.

How it works

ŒPÇÐfS€Ṃ     Main link. Left input: T (list). Right input: L (integer).

ŒP           Powerset; generate all subsets of T.
   Ðf        Filter them...
  Ç            applying the helper link.
     S€      Compute the sum of each kept subset.
       Ṃ     Take the minimum.

³œ-;⁴Ṃ;¹S>⁴  Helper link. Input: A (subset of T)

³œ-          Multiset subtraction; remove the elements of A from T, counting
             multiplicities.
   ;⁴        Append L to the resulting list.
     Ṃ       Take the minimum.
             If S == T, the difference was empty and the minimum is L.
      ;¹     Prepend the minimum to A.
        S    Compute the sum.
         >⁴  Compare it with L.
             If S == T, the comparison will return 1.