The need
Proofreading, bulk word changes, or splitting the job between several people — all of that moves much faster in a sheet than in plain text. SRT itself is plain text, but its cue structure (index, timing, dialogue) maps neatly onto four spreadsheet columns.
Where to do it
Open Subtitle ⇄ table conversion, switch to "to table", drag in the SRT, and the preview fills with one row per cue across four columns — index, start, end, text. Hit "Download Excel (.xlsx)" and it is yours. VTT is supported the same way.
When you are done editing: switch the mode to "to subtitle", put the sheet back in, and you get an SRT again. The rule is three columns for start, end and text (English Start / End / Text work too), in any order.
Common pitfalls
Fix broken encoding first: this page reads UTF-8 only. A screenful of question marks or boxes means a trip to Mojibake repair first.
CSV or xlsx: choose .xlsx when the file is going into Excel, so the time column cannot be reformatted; CSV is more portable but Excel may read it as something else — set the time column to "Text" if that happens.
ASS does not work: ASS carries style directives, so convert it to SRT before putting it in a table.
Related
The full two-way walkthrough — How to convert subtitles to Excel / CSV; translating afterwards — Subtitle translation; a last pass before delivery — Subtitle QC.