SharePoint 2007 does not support crawl schedules larger than 24 hours. So if you want to schedule a crawl to run every 36 hours, by default there is no way to do this.
At a customer we had a very large environment, which had a huge amount of changes on a daily bases. A crawl during the weekend took just a few minutes, but during the week this increased to 32 hours. Because Microsoft also recommends not to start a crawl when the previous crawl is still running (even though it cannot run two instances of the same crawl, SharePoint does something that can break the index before it detects the crawl is already running), I have created a script that does this for me.
The script checks if a crawl is running and if so quits. If a crawl is not running, it starts another incremental crawl. By scheduling this script every 15 minutes, I can make sure the crawl is never stopped for more than 15 minutes.
How to use the script:
- Download the PowerShell script
- (If necessary) Change the Content Source name
- Run or schedule the script