I ask because I need something translated and have it sound aristocratic. There's a voodoo spirit/saint/angel that doesn't like speaking anything other than French and is most commonly associated with French Noblewomen. freetranslation.com says Vous ne devriez pas attendre si longtemps entre l'appel is French for "You shouldn't wait so long between calling" However, I speak Spanish pretty well and know that that site doesn't translate grammar or context properly. I can assume that it doesn't do French very well either. After this, the spirit speaks English, but as a matter of formality, I need her to greet and scold my protagonist in French before speaking to him. The greeting I know because I've heard it before, but this part I have not.
I speak French well enough, but perhaps not well enough to sufficiently elevate your intended diction. This said the first half of your phrase appears suited to the task in hand. I would query the "... entre l'appel" part however as it seems to miss your intent. With such queries you may be best trying a French translation-type forum rather than our general one. In my experience the majority of the members at wordreference.com are quick and reliable.
I agree with Gannon. Also, professional translators (like Wreybies) are not expensive, especially for a one-time fee to get your story correct.
I studied French for 5 years but that was quite a while ago. I would think the following are acceptable: Vous ne devriez pas attendre si longtemps entre les appels. (between calls - uses the noun) Vous ne devriez pas attendre si longtemps entre le fait d'appeler. (between calling - uses the verb)
I study french currently and i have to agree with NaCl. "vous" indicates formality but im not sure what the most formal "tense" is. (that may not be the right term for it). I think the first one "vous ne devriez pas attendre si longtemps entre les appels" fits best. I ran this by my french professor and she agrees that the first would be the best. the second translates more towards "you should not wait so long between the calling." The sentence you have off the translator says that there is only one call, which make sense, i dont think, for you. hope this helps, Birdi