Вот код, если сместить if response=='сегодня' к остальным, то оно прекрасно работает, но нужно чтобы после нажатия на группу и кнопку расписания происходила выдача 
from vk_api.longpoll import VkLongPoll, VkEventType
from vk_api.keyboard import VkKeyboard, VkKeyboardColor
import vk_api
import random
import xlrd
from datetime import date
from datetime import datetime
token ='токен'
vk_session = vk_api.VkApi(token=token)
session_api = vk_session.get_api()
longpoll = VkLongPoll(vk_session)
def create_keyboard(response):
    keyboard = VkKeyboard(one_time=False)
    if response == 'начать':
        keyboard.add_button('Список групп', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('Поиск по преподавателю', color=VkKeyboardColor.POSITIVE)
    elif response == 'назад':
        keyboard.add_button('Список групп', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('Поиск по преподавателю', color=VkKeyboardColor.POSITIVE)
    elif response == 'поиск по преподавателю':
        keyboard.add_button('Назад', color=VkKeyboardColor.NEGATIVE)
    elif response == 'список групп':
        keyboard.add_button('1 Курс', color=VkKeyboardColor.DEFAULT)
    elif response == '1 курс':
        keyboard.add_button('ТМ1', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('ВС1', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('ИС1', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('ЭЛ7', color=VkKeyboardColor.DEFAULT)
        keyboard.add_line()
        keyboard.add_button('Ю45', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('М116', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('ПР23', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('В23', color=VkKeyboardColor.DEFAULT)
        keyboard.add_line()
        keyboard.add_button('Х182', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('Х183', color=VkKeyboardColor.DEFAULT)
        keyboard.add_button('Ю40', color=VkKeyboardColor.DEFAULT)
        keyboard.add_line()
        keyboard.add_button('Назад', color=VkKeyboardColor.NEGATIVE)
    elif response == 'тм1':
        keyboard.add_button('Сегодня', color=VkKeyboardColor.DEFAULT)
        keyboard.add_line()
        keyboard.add_button('Завтра', color=VkKeyboardColor.DEFAULT)
        keyboard.add_line()
        keyboard.add_button('На неделю', color=VkKeyboardColor.DEFAULT)
        keyboard.add_line()
        keyboard.add_button('Назад', color=VkKeyboardColor.NEGATIVE)
    keyboard = keyboard.get_keyboard()
    return keyboard
def send_message(vk_session, id_type, id, message=None, keyboard=None):
    vk_session.method('messages.send',{id_type: id, 'message': message, 'random_id': random.randint(-2147483648, +2147483648), 'keyboard': keyboard})
for event in longpoll.listen():
    if event.type == VkEventType.MESSAGE_NEW:
        print('Сообщение пришло в: ' + str(datetime.strftime(datetime.now(), "%H:%M:%S")))
        print('Текст сообщения: ' + str(event.text))
        print(event.user_id)
        response = event.text.lower()
        keyboard = create_keyboard(response)
        if event.from_user and not event.from_me:
            if response == 'начать':
                send_message(vk_session, 'user_id', event.user_id, message='Привет!', keyboard=keyboard)
            elif response == 'список групп':
                send_message(vk_session, 'user_id', event.user_id, message='Список групп', keyboard=keyboard)
            elif response == '1 курс':
                send_message(vk_session, 'user_id', event.user_id, message='Список групп 1 курса', keyboard=keyboard)
            elif response == 'поиск по преподавателю':
                send_message(vk_session, 'user_id', event.user_id, message='Введите фамилию преподавателя', keyboard=keyboard)
            elif response == 'назад':
                send_message(vk_session, 'user_id', event.user_id, message='Привет!', keyboard=keyboard)
            elif response == 'тм1':
                if response == 'сегодня':
                    today = datetime.now()
                    day = date.weekday(today)
                    if day == 0 :
                        workbook = xlrd.open_workbook(r"ras19-20_2s.xls")
                        sheet = workbook.sheet_by_index(0)
                        def get_cell_range(start_col, start_row, end_col, end_row):
                            return [sheet.row_slice(row, start_colx=start_col, end_colx=end_col + 1) for row in range(start_row, end_row + 1)]
                        data = get_cell_range(3, 7, 6, 26)  # D8 to G27
                        print (data)
                        send_message(vk_session, 'user_id', event.user_id, message=str(data), keyboard=None)
                    elif day == 3 :
                        workbook = xlrd.open_workbook(r"ras19-20_2s.xls")
                        sheet = workbook.sheet_by_index(0)
                        def get_cell_range(start_col, start_row, end_col, end_row):
                            return [sheet.row_slice(row, start_colx=start_col, end_colx=end_col + 1) for row in range(start_row, end_row + 1)]
                        data = get_cell_range(3, 7, 6, 26)  # D8 to G27
                        print (data)
                        send_message(vk_session, 'user_id', event.user_id, message=str(data), keyboard=None)
                send_message(vk_session, 'user_id', event.user_id, message='123', keyboard=keyboard)