In some situations your LUX dashboard may display an error saying "Query timed out". LUX queries are executed across billions of page views, so it's possible in some situations for the query to exceed the maximum query time limit. The main factors that make queries take a long time are:
time range - If you query for one month of data and it times out, try reducing it to one week.
stat - Our distributed database architecture is great for calculating averages across large amounts of data, but median and 95th percentile take much longer to calculate. Try switching to average, or reducing the time range.
Another tactic is to break your query up into smaller time ranges. LUX caches query results, but if your query always times out then there's nothing to cache. If your one month query keeps timing out, reduce the time range to 1 week, then 2 weeks, etc. Each week of results is cached, so now your one month query will complete successfully because it's using the cache. In addition, each day when you view the same dashboard it only needs to retrieve a single day of new data, so it will continue to work without timeouts.