Indefinite

Not definite. Undefined. Ambiguous. Not clear or understandable. Incomprehensible.

Indefinite period of time is an arbitrary length of time with no clear beginning or end. Could be eternal.

Indefinitely

(in)def·i·nite·ly

en/ˈdef(ə)nətlē/

1.
without doubt (used for emphasis). Inner side of a person, object or thing
certainly
surely
for sure
unquestionably
without/beyond doubt
without/beyond question
beyond any doubt
undoubtedly
indubitably
assuredly
positively
absolutely in a definite manner; clearly.
inner side of something.
interior
inner part
2.
the inner part; the interior.
situated in, or derived from, the inside.
inner
interior
internal
inmost
innermost

Setting: (nightlife in a bar)

Guy walks up to a girl in a bar....
Guy: "Do you know when I am indefinitely?"

Girl:"Indefinitly?"

Guy:"When my balls are smackin you, in the ass! That's when I know, I am IN DEFINITLY"!

GIRL: "Do you know when YOUR indefinitely?"

GUY:"Indefinitly?"

GIRL:"When your balls are smackin me, in the my ass! That's when I know, your IN DEFINITLY"!

Pick up line that works to both his & hers advantage.