Apologies for the late reply. Check interval (in terms of seconds) determines how frequent the router will check for SIM Switch conditions. However, Attempts before SIM Switch (in terms of iteration), determines how many times the router will check if the conditions is actually met. In summary, Check interval will be used first before Attempts before Sim Switch.
For example, Check interval is set to 5 seconds and Attempts before sim switch is set to 2. This means that every 5 seconds, the router will check if one Sim switch conditions are met. If condition is satisfied, then the router will confirm twice if it actually meets the condition. Hope this clarifies your query.