Your partner can land whenever they want, as long as it's before the COPR expires. There's no requirement to stay in Canada afterwards (other than needing to live in Canada 2 out of every 5 years to maintain PR, although condition 51 might muddy that rule up a bit.) There have been lots of cases of people landing for a weekend, getting a SIN card and then going back home to keep working until they could find a job in Canada, or to finish their schooling.
If your partner is not ready to settle, do the landing procedure with the B4a form (goods to follow) - this allows your partner to move their things into Canada later without worrying about duty. Also, COPR isn't good for re-entry, so when your partner is ready to really move into Canada they will need to apply for a travel document if they haven't received their PR Card yet. Although, someone can correct me if I'm wrong, but that doesn't apply to people crossing by land borders.
In terms of Condition 51, I am under the impression it really is only a risk if you and your partner live at 2 separate addresses for an extended period of time. It's really up to you to follow the condition of living together after landing for 2 years, as best you can. If it would only take a couple of months to get your partner ready to really settle, you shouldn't worry I wouldn't think.