The optimization process and recommendations:

1. Avoid Calling Functions With Indexed Columns (query line: 35): When a function is used directly on an indexed column, the database's optimizer won’t be able to use the index. For example, if the column `EmployeeID` is indexed, the index won’t be used as it’s wrapped with the function `LEN`. If you can’t find an alternative condition that won’t use a function call, a possible solution is to store the required value in a new indexed column.
2. Create Optimal Indexes (modified query below): The recommended indexes are an integral part of this optimization effort and should be created before testing the execution duration of the optimized query.
3. Explicitly ORDER BY After GROUP BY (modified query below): By default, the database sorts all 'GROUP BY col1, col2, ...' queries as if you specified 'ORDER BY col1, col2, ...' in the query as well. If a query includes a GROUP BY clause but you want to avoid the overhead of sorting the result, you can suppress sorting by specifying 'ORDER BY NULL'.
4. Remove Redundant Left Joins (modified query below): Redundant LEFT JOINs (e.g. `SiteMaster`) were detected in the query. Removing them will result in a performance improvement. In some cases, JOINs become redundant after an optimization is applied, such as when converting OR conditions to a UNION clause.
5. Remove Redundant Left Joins (modified query below): Redundant LEFT JOINs (e.g. `Accounts`) were detected in the query. Removing them will result in a performance improvement. In some cases, JOINs become redundant after an optimization is applied, such as when converting OR conditions to a UNION clause.
6. Remove Redundant Left Joins (modified query below): Redundant LEFT JOINs (e.g. `DriveMaster`) were detected in the query. Removing them will result in a performance improvement. In some cases, JOINs become redundant after an optimization is applied, such as when converting OR conditions to a UNION clause.

Optimal indexes for this query:

ALTER TABLE `People` ADD INDEX `people_idx_personid` (`PersonID`);
ALTER TABLE `PeopleStaffingDetail` ADD INDEX `peoplestaffingdeta_idx_personid` (`PersonID`);
ALTER TABLE `PeopleStaffingRoleDetail` ADD INDEX `peoplestaffingrole_idx_personid_roleid` (`PersonID`,`RoleID`);
ALTER TABLE `StaffingEventMaster` ADD INDEX `staffingeventmaste_idx_eventid` (`EventID`);
ALTER TABLE `StaffingEventShiftDetail` ADD INDEX `staffingeventshift_idx_shiftid` (`ShiftID`);

The optimized query:

SELECT
        PEVD.EmployeeID[EmployeeID],
        P.PersonID,
        SEM.eventbegindate[EventDate],
        
    LEFT(CONVERT(varchar(20),
    MIN(PSD.StartTime),
    108),
    5)[StartTime],
    LEFT(CONVERT(varchar(20),
    MAX(PSD.EndTime),
    108),
    5)[EndTime],
    CASE 
        WHEN DAY(MIN(PSD.StartTime)) <> DAY(MAX(PSD.EndTime)) THEN 1 
        ELSE 0 END[IsAddDay] FROM
    StaffingEventMaster SEM 
INNER JOIN
    StaffingEventShiftDetail SESD 
        ON SEM.EventID = SESD.EventID 
INNER JOIN
    PeopleStaffingDetail PSD 
        ON SESD.ShiftID = PSD.ShiftID 
INNER JOIN
    People P 
        ON PSD.PersonID = P.PersonID 
INNER JOIN
    PeopleEmployeeValueDetail PEVD 
        ON PEVD.PersonID = P.PersonID 
INNER JOIN
    PeopleStaffingRoleDetail PSRD 
        ON P.PersonID = PSRD.PersonID 
        AND PSRD.RoleID <> 153 
WHERE
    LEN(PEVD.EmployeeID) > 0 
GROUP BY
    PEVD.EmployeeID,
    P.PersonID,
    SEM.EventBeginDate 
ORDER BY
    NULL