So the Crown refused to drop the charge (they rarely do). Now you have to go to trial and fight for dismissal on the grounds that the information on the face of the ticket has deprived you of some right. The crown must prove the correct date and place of the offense (within reason). The date will likely be correct on the officers notes, but it's the date on the ticket that matters to you. The ticket is the "charging document" and must stand on its own to convict you.
The problem is going to be that you can't deny that you were the person stopped. And I doubt anyone would consider the possibility that the speed limit was different on the date of the citation from the date of the traffic stop, so the JP may deny your motion. But it appears to be your only chance to beat the ticket. Because you're dealing with a "technicality" here, you might want to consider using a paralegal who has experience arguing procedural matters.
You file your objection before you enter your plea. If you do not object, the court will consider the defect to be accepted by the defendant, and the trial will continue.
If the court allows an amendment and another trial date is set, the defense can request costs relating to missed work, traveling expenses, etc.
Provincial Offences Act
37. Where the information or certificate is amended or particulars are ordered and an adjournment is necessary as a result thereof, the court may make an order under section 60 for costs resulting from the adjournment. R.S.O. 1990, c. P.33, s. 37.
If your looking for an easy way out, there isn't one! Arguing for dismissal on the basis of a defect is best left to an expert. Most defects are considered "minor" and will be amended by the court. As I said previously, there are cases where an amendment has been refused when NO date is listed. You need to find out if the WRONG date is treated the same way.
If this is your first time in court, I'd suggest using a Paralegal experienced in traffic court.