C＃：等待异步操作完成固定的时间，然后根据结果执行一些操作

Question

在Asp.Net Core控制器中，我想执行以下操作：

// Start preparing a report as string:
string reportText = await ReportService.PrepareAsync();

// wait for 10 seconds; how?
if (secondsPassed > 10) 
{
    // When finished, save the report text to database,
    // and notify a user by SignalR
}
else 
{
    // Report finished within 10 seconds; 
    // return immediately as a json response
    return Ok(new { Report = reportText });
}

建议完成上述或类似任务的方法是什么？