Why is "cuando quiera" two words?
Spanish has the words cualquiera, dondequiera, quienquiera, and even siquiera, but not cuandoquiera. Is there a reason for this?
Actually mountaingirl was totally wrong. "Cuandoquiera" is a valid Spanish word and is written as a single word when meaning "whenever"; the phrase "cuando quiera" means roughly "when he/she/it/you (formal singular) might/should desire" and is the same as saying e.g. "cuando desee." They're not the same thing.
See here: http://www.fundeu.es/recomendacion/cuandoquiera-y-cuando-quiera-no-son-lo-mismo-795/
The one word examples you cited all contain a single concept: whichever, wherever, whomever, and at least. On the other hand, "cuando quiera" retains the meaning of the verb, and would be translated as "whenever you/he/she want". The subjunctive form of "querer" gives the "whenever" feeling to the "cuando". Hopefully this helps! Languages aren't always logical, and that's what makes them fun in a challenging sort of way!
Along the same lines there is conmigo, contigo, and consigo for with me, with you, with you(formal). Yet there is no sinmigo, sintigo or sinsigo. Only sin mi, sin ti, and sin Ud., for without me, without you. etc.
So don't look for logic.
This link also offers an explanation.
I guess what I don't understand is that "whenever" means the same thing in time that "wherever" means in space.