am running a study that tracks train time delays. 'Delay' is defined as being at least $10$ min past the scheduled time of arrival $-$ and I note down the proportion of trains that were delayed.I do not include the magnitude of the actual delay in my report. My data is being measured in which way and which SQC chart should I use if I wish to monitor the delays?

As Attribute data $-$ use p charts

As Variable data $-$ use Xbar and R charts