esx_core/[core]/cron/server/main.lua

local Jobs = {}
local LastTime = nil

function RunAt(h, m, cb)
    Jobs[#Jobs + 1] = {
        h = h,
        m = m,
        cb = cb,
    }
end

function GetUnixTimestamp()
    return os.time()
end

function OnTime(time)
    for i = 1, #Jobs, 1 do
        local scheduledTimestamp = os.time({
            hour = Jobs[i].h,
            min = Jobs[i].m,
            sec = 0, -- Assuming tasks run at the start of the minute
            day = os.date("%d", time),
            month = os.date("%m", time),
            year = os.date("%Y", time),
        })

        if time >= scheduledTimestamp and (not LastTime or LastTime < scheduledTimestamp) then
            local d = os.date('*t', scheduledTimestamp).wday
            Jobs[i].cb(d, Jobs[i].h, Jobs[i].m)
        end
    end
end

function Tick()
    local time = GetUnixTimestamp()

    if not LastTime or os.date("%M", time) ~= os.date("%M", LastTime) then
        OnTime(time)
        LastTime = time
    end

    SetTimeout(60000, Tick)
end

LastTime = GetUnixTimestamp()

Tick()

AddEventHandler("cron:runAt", function(h, m, cb)
    assert(type(h) == "number", ("Expected number for h, got %s"):format(type(h)))
    assert(type(m) == "number", ("Expected number for m, got %s"):format(type(m)))
    assert(type(cb) == "function", ("Expected function for cb, got %s"):format(type(cb)))

    RunAt(h, m, cb)
end)