Make sure you turn on Regex mode:
Search:
Code:
<p class="timebreak"> <br class="calibre1" /></p>\s*<p class="timebreak">
Replace:
Or if there are many calibre#s (and not just "calibre1" in that position), you will want to use this Search instead:
Code:
<p class="timebreak"> <br class="calibre[0-9]+" /></p>\s*<p class="timebreak">
Red section says look for any "calibre", followed by one or more 0-9. This means it will match "calibre1", "calibre2", .... "calibre99999".
Blue section says look for zero or more "white space".
WARNING: Whenever using Regex, be extremely careful, and
DO NOT use "replace all" until you have manually done "Replace" "Replace" "Replace", paying careful attention to make sure everything is working correctly. Save a copy of the EPUB before you go use Regex.