Hey here is my explanation:
“平时”=usually/normal
eg.我平时喜欢读一些名著=i usually like reading some classic
“届时”=on the occasion/ at the scheduled time, it's more formal (for some big events or formal meetings or Wedding or funeral)
eg. 我届时一定会参加你的婚礼。=I will definitely attend your wedding.
“及时”=timely
eg.你的及时帮助,才让我度过了难关。=Your timely help helped me through the difficulties.
“准时”=“按时”=on time
eg.Please come to class on time tomorrow.=请你明天准时来上课=请你明天按时来上课。
Hope i have made it clear. Any help you can contact me.
(more)“平时”=usually/normal
eg.我平时喜欢读一些名著=i usually like reading some classic
“届时”=on the occasion/ at the scheduled time, it's more formal (for some big events or formal meetings or Wedding or funeral)
eg. 我届时一定会参加你的婚礼。=I will definitely attend your wedding.
“及时”=timely
eg.你的及时帮助,才让我度过了难关。=Your timely help helped me through the difficulties.
“准时”=“按时”=on time
eg.Please come to class on time tomorrow.=请你明天准时来上课=请你明天按时来上课。
Hope i have made it clear. Any help you can contact me.