Example repro:

1. emacs -Q

2. C-x * *

3. t N

4. ' 1.5hr RET

5. +

Expected:

1: <2018-03-22 Thu 02:30>

Got:

1: <2018-03-22 Thu 01:00> + 1.5 hr

Emacs : GNU Emacs 27.0.50 (build 7, x86_64-pc-linux-gnu, GTK+ Version 3.22.28)

of 2018-03-19

Package: Calc