If Your web hosting company do not offer a cronjob service, then You have to use an external/remote cronjob provider.
To use the calendar, You don't need to set up a cronjob, but when You want automatic mailing/advice and/or automated backup routines, You need a cronjob.
My sites are hosted at one.com - and they do not offer a cronjob service.
Their service is free, and it is easy to setup a cronjob.
Execution up to 60x an hour
Set up as many cronjobs as you like. Each of your jobs can be executed up to 60 times an hour. Flexibly configure the execution intervals. Password-protected and SSL-secured URLs are supported.
If you like, we can inform you by email in case a cronjobs execution fails or is successful again after prior failure. You can find detailed status details in the members area.
View the latest executions of your cronjobs including status, date and time, durations, and response (header and body). You can also view the three next planned execution dates.
Setting up the cronjob in LuxCal is quite easy.