fix(builder): keep the time of day when a zone item is combined with a relative item

[sylvestre]

follow up of #320

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.34%. Comparing base (390c747) to head (1c2efe4).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #324 +/- ##
==========================================
- Coverage 99.34% 99.34% -0.01% 
==========================================
Files 21 21 Lines 4125 4123 -2 Branches 136 136 ==========================================
- Hits 4098 4096 -2 
Misses 26 26 Partials 1 1 

Flag	Coverage Δ
macos_latest	99.34% <100.00%> (-0.01%)	⬇️
ubuntu_latest	99.34% <100.00%> (-0.01%)	⬇️
windows_latest	13.72% <0.00%> (+<0.01%)	⬆️

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