Mozilla requires code review for all code changes, too. Time zones are a big challenge because many employees work remotely and few feature teams are collocated

Mozilla requires code review for all code changes, too. Time zones are a big challenge because many employees work remotely and few feature teams are collocated in the same office. Engineers have to accept some latency, like you describe. To keep their pipeline full, an engineer typically must multitask multiple bugs in different stages of the review process. Reviewers try to prioritize requests from volunteer contributors so they don't get discouraged. These reviews often require extra feedback on basics of patch creation or coding style. Over time, some experienced volunteer contributors become reviewers, too. Instead of requesting review from a specific individual, some teams have experimented with assigning some review requests to a team alias. Anyone on the team who is available or has some free time can approve and land the patch. This works well for small patches that don't depend on specific expertise. This process also depends on everyone sharing the review burden.