【HELP】Can not configure the cron(schedule) value of a process

[foggiest]

I have a new created process,and i want to config its cron(schedule) infomation,
so i click the cron(schedule) button in this process's definition to entry configure page ,as the picture shows below

after i entered the cron config page,i wanted to modify the cron value which has the default value of " 0 0 * * * ? * "
so i clicked on the cron value bar, and the page showed

then i clicked on the "specific hours" dropdown options and i wanted to choose a certion hour like 11,
but the dropdown options hid(or retracted/disappeared) right after i clicked on it,within a second, made it almost impossible for me to locate the hour value that i want
i repeated the operation for another dozens of times in different web browsers (edge/chrom), and it ended up in vain

Is this a bug?And how can i configure a process's cron(schedule) value with specified hours(minuts/days...) in the web page