• Would this do?

    select *

    from @Energy_Centre_Availability ECA

    inner join @Energy_Centre_Boiler_Maintenance_Schedule ECBMS

    on ECA.t_stamp >= ECBMS.StartDate

    and ECA.t_stamp < ECBMS.EndDate

    ** Don't mistake the ‘stupidity of the crowd’ for the ‘wisdom of the group’! **