Take off a moment to indulge in an afternoon nap when it's most muggy (9)

'take off a moment to indulge in an afternoon nap' is the definition.
I can't judge whether this definition defines the answer.

'when it's most muggy' is the wordplay.
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'most' means to remove the first letter.
'muggy' becomes 'ickiest' (I am not sure about this - if you are sure you should believe this answer much more).
'as'+'t'='ast'
'ast' with its initial letter removed is 'st'.
'st'+'ickiest'='STICKIEST'

Can you help me to learn more?