Working Hours - line managers asking for exceptions to the rule

I am working in a travel company based out of Europe. Our employees work in very good atmosphere with all benefits like weekly TGIF's, quarterly Grand TGIF's, 5 days working, 8.5 hours of shift, and Indian and European holidays along with 1CL and 1PL every month. In short, its like dream job.
We don't have any HR department, I take care of day to day Admin work and basic HR work, like file maintaining, Policy implementation, attendance, and other day to day work. in short HR cum Admin.
Our company gives leverage of 30 mins, before it is marked RED and 4th Red is considered is 1 Full day leave deduction for the quota of 24 ( PL+CL of year).
Few employees come consistently late by 25-29 mins and hence, they are not marked red. and few who come late sit back late to give extra login hours 9, 9.5 or some time 10 hours to justify their late coming. Though being travel company is it some time specially during season is required to work till late ( different time zone), but what should I do with those, including their TL and managers having habit of late coming but saving them selves from red mark, and if there is red mark then their line manager will mail to consider this exception and not deduct leave balance.
I wish to mark general e-mail mentioning all this but not pin pointing any one.

A policy decision has to be taken to remove this 30 minute buffer.
One needs to see why this buffer was given?
By practise it becomes the new IN time.
Let the top brass decide and then remove this buffer in gradual manner.

Where is this company located. I am also from travel field would want to work in your company.

Hello ,
In my view there is no need to give 30 min buffer , 1st you have to remove it, because sometimes employees take unwanted advantages for the liberality of policies. lets take a example if someone is coming on every other day by 25-29 min late , but he/she would not be come in late comers and not count as red, they easily can save their leave balance as well. up to 5-15 min relaxation can be justified for a limit like 3 -4 , afterwards every single late should be count as an absent or half day . you should also take care about the honest and hard working employees those can be late due to some issue or emergency but depute long hours in office to complete the task on time.
Making a policy can be helpful for you.

Send them a mail like this:
Dear Employees ,
It has been observed that many employees are coming to work late in the morning. Everyone is required to be in office before the office start time.
The office timings are from 10.00 a.m. to 7.00 p.m. from Monday to Saturday. Lunch Hour shall be 45 Mins.
If an employee is running late, he/she needs to inform the HR.
Employees will be allowed to report to duty 10-15 mins late 2 to 3 times in a month, though do not make it a practice.
This Attendance practice will be tracked on a monthly bases & if still there is a late coming practice by the employees,strict disciplinary action will be taken.
3 times late punch: Acceptable
4th time late Punch: Marked Red & treat it as a warning
5th time or more : 1/2 day salary Deduction
Punctuality & Time Management are part of the organisation Culture.
Kindly Co operate and be punctual for the advancement and progress of our organisation.