Can I say a later bus? Or should I say a latter bus? For example I was in a hurry to catch a ... bus to the city centre.
Yes there are.
When using a list of items you can say the former and latter ONLY if that list comprises TWO items. Do not use A, B and C, of which the latter, as that is not grammatical.
When using a list of two items, "I am thinking about cooking and ordering food, but I already decided to do the latter." then it is grammatical to use the word "latter". The same applies to former. (Source: The blue book of grammar 11th edition by Jane Straus, page 95, confusing words and homonyms. The exact example in the book is this, "He offered a trip to New York, Chicago, or Tarzana. She chose the latter. Oh no she didn't. Latter can't be used when there are three (or more) options. It applies only to sentences like 'He offered a trip to New York or Tarzana, which makes New York the former, Tarzana the latter.' When there are more than two people or things mentioned, use last
Your question asks about "later" as well. Later means more time has passed, this has nothing to do with the others (semantically speaking), but the spelling and phonetics of the word are very similar; therefore, the category confusing words and homonyms applies perfectly. It is a confusion based on how the word sounds and is written down, but the meaning of the words latter and later differ, the for latter meaning time and the former meaning something out of my two part list.