There isn’t a universal optimal duration for an influencer campaign to maximize both reach and engagement as various factors come into play. The key factors include:

1. Platform: The social media platform used by the influencer. For instance, campaigns on Instagram may require a different duration compared to YouTube due to each platform’s unique user behavior and content requirements.

2. Content Strategy: The kind of content being shared and the frequency. Some campaigns may involve a series of posts over several weeks, while others may revolve around a single impactful post or event.

3. Audience: The audience’s behavior and engagement patterns on the influencer’s profile. Certain audiences might be quicker to engage with content, while others may need more time to interact.

4. Goals: The objective of the campaign. If it’s for brand awareness, a longer, steady campaign might work better. For a product launch, a short, intense burst could be more effective.

What’s crucial is to monitor campaign performance in real-time, adjust accordingly and learn from the results for future campaigns. Using a powerful influencer marketing platform like Flinque could help brands and influencers track analytics, measure engagement, and adjust campaign durations as per the need.

Remember, no ‘one-size-fits-all’ exists in influencer marketing. It’s all about finding what works best for your specific circumstances. This largely comes down to strategic planning, execution and ongoing monitoring/optimization, all of which can be significantly enhanced by leveraging the right influencer marketing platform.