no one to wait for them or excuse them for being late
This is a custom that is not familiar to UK and the States. You give one example but I am still perplexed.
You also start off in a puzzling way, saying 'relaxed way of life' yet 'never late' which suggests 'driven' personalities.
You then give the sentence above which is bewildering to us. 'No one to wait for us ' - but everybody at the conference is waiting for people to get there so they can start - and no one to excuse us?? Who is this nursemaid who is going to stand up and apologize for me??
What then eventuates is that, yes, they are late, but this custom comes into play so that it is not seen as 'being late' or, 'is excused'.
I'll have to clear my mind and come back with fresh logic on this one! But you need to alert the reader at the outset eg
Bulgarians have a rather relaxed pace of life, tempered with an idiosyncratic approach to/concept of punctuality.
then give examples of the differences eg never to late in this situation, yet in that situation something else would happen. Then how this is viewed from a Bulgarian perspective - why it is socially acceptable to Bulgarians.