You don't have to strictly abide by the 30 day guideline - what you have to do is make sure that this
Application to Change Conditions or Extend my Stay in Canada is received by CIC prior to the expiration date on his current VR - so my suggestion is always that people send it to Vegreville via courier and get delivery tracking and confirmation so that you have proof it was received on time. This will give your fiance "implied status" to remain in Canada until they assess the extension request and notify him of the decision - which takes about 100 days. If he leaves Canada in the interim, the "implied status" is invalidated - and so would be his VR if he was to leave before March 14th.
The important thing to remember is that, in order for his status to be extended, you have to have already gotten married before it's submitted. You can't just submit one asking for more time because you want to get married - you have to get married. He has to have a valid reason for remaining in Canada and short of being eligible as an applicant for permanent status, there isn't one. Basically they issued this VR to "put him on notice" that he can't just stay in Canada past the time he's authorized (six months for visa-exempt nationals unless they say otherwise on entry) without either leaving or submitting an application to extend. This was, basically, a slap on the wrist - they could have refused him entry or excluded him from Canada if they wanted to be nasty about it - so he was, indeed, lucky. So, if the two of you are getting married, you need to do that asap, submit the extension application with proof of that, and then get his paperwork in order to apply for permanent residence. There's a lot you need to know about
that process - i.e. filing outland as opposed to inland, even if he wants to stay with you in Canada during processing, etc., - so please be sure to come back and get advice about this before you start filling out PR application forms. But first things first for now.
When you/he submits the application for extension, you need to be able to include with the extension application a copy of your marriage licence (or record of solemnization because you won't have the certified copy of the m/l in time) and proof that you are applying to sponsor him for PR. This could be in the form of a copy of the receipt for payment of the mandatory PR fees of $550 (payment of the $490 Right of Permanent Residence fee can be deferred until later on during processing of the PR ap). You'll also need a letter from your employer (which you'll need for the PR ap anyway) that shows you have a job and are able to support him. If he's intending to stay, you should know that it will take approximately 6 months (sometimes a bit less depending on the visa office) to finalize the PR process and he won't be able to work in Canada during that time. (Don't be fooled into applying via the inland process because of promises of an open work permit - it takes at least 6 months time for the inland application to even be assessed as valid for issuing an OWP, so he'd be unable to work for that long for sure with the inland process AND he wouldn't be able to go back home, if you guys needed him to work, and maintain that inland PR ap, too.) There is a fee for extension as a visitor (which is all he's eligible for) of $75. They will assess his request and get back to you in about 3 months time - in the meantime, as I mentioned before, he can remain in Canada under the conditions of the original VR (except the expiration) but he can't work or enroll in school, etc. In addition, that VR is not a re-entry permit - none of them are - so if he leaves Canada, it will not guarantee him the ability to enter again . . . even if he leaves prior to its expiration. See, the IO who issued it might have implied that but the bottom line is - they won't know if or when he leaves. There's no record kept of departures unless he's specifically told to report to them before he goes. So, when he comes back again, he will have no way to prove that he complied with the terms of this stay . . . which is why I don't believe for one minute that there's any such thing as "building a rapport" with them to lift a restriction . . . he's going to be flagged from now on and he'll be pulled into secondary anytime he tries to enter Canada between now and when he finally has permanent status.