What does the cryptic crossword clue "Preparing day for mobilising amid turbulent reign (8)" mean?

The definition is "Preparing". The wordplay uses an anagram. anagram of DAY + REIGN = READYING; definition: "Preparing" The answer is READYING.

Preparing day for mobilising amid turbulent reign (8)

Daily Mail Cryptic #17542 | 10 Across | 2025-01-28 flower