def get_start_time(schedules, duration):
    print(schedules, duration)
    time_management = [["{:02d}".format(i), [int(l) for l in range(0, 60) if i != 19]] for i in range(9, 20)]

    for row in schedules:
        for time in row:
            if time[0][3:].startswith("0") and time[0][3:] != "0":
                time[0] = time[0][:3] + time[0][4:]
            elif time[1][3:].startswith("0") and time[1][3:] != "0":
                time[1] = time[1][:3] + time[1][4:]

    for row in schedules:
        for time in row:
            scope = []
            for elem in time_management: ##Находим индексы schedules в timemanagement
                if elem[0] == time[0][:2]:
                    scope.append(time_management.index(elem))
                if elem[0] == time[1][:2]:
                    scope.append(time_management.index(elem))

            if scope[0] == scope[1]:
                for j in range(int(time[0][3:]), int(time[1][3:])):
                    time_management[scope[0]][1][j] = 'x'
            elif scope[0] != scope[1]:
                for i in range(scope[0], scope[1] + 1):
                    if i == scope[0]:
                        for j in range(int(time[0][3:]), 60):
                            time_management[i][1][j] = 'x'
                    elif i == scope[1]:
                        for j in range(int(time[1][3:])):
                            time_management[i][1][j] = 'x'
                    else:
                        for j in range(60):
                            time_management[i][1][j] = 'x'
    scope = []
    counter = 0
    for block in time_management:
        for i in range(len(block[1])):
            if block[1][i] != 'x':
                counter += 1
                if counter == 1:
                    scope.append(block[0])
                    scope.append(block[1][i])
                    print(scope)
                if counter == duration:
                    return str(scope[0]) + ":" + "{:02d}".format(scope[1])
            else:
                scope = []
                counter = 0
    return None
    return None