Hello Toan,
I’m not very familiar with crontab but Open Embedded does support a Cron daemon for executing programs at set times.
You can add it by adding the cronie package. To do this you may add the following line on the conf/local.conf file inside your build directory:
IMAGE_INSTALL_append += " cronie "
You can find more information on the recipe description:
https://github.com/openembedded/openembedded-core/blob/zeus/meta/recipes-extended/cronie/cronie_1.5....
I hope this helps!
Regards,