This question has previously been asked and answered on ELU. To summarise, there are three different syntactic constructions for the verb allow...
1: With a gerund complement indicating what is allowed:
Mama don't allow no drumming (non-standard English for Mama doesn't allow [any] drumming)
Nor does she allow smoking reefers (perfectly valid example of a gerund complement)
This construction does not normally accept a patient/object (the person/thing being allowed to do something). You sometimes see things like "She doesn't allow JJ Cale smoking reefers", but most native speakers do not like that much (it should be "She does not allow JJ Cale to smoke reefers", per #3 below).
2: With a noun phrase object indicating what is allowed:
Some states do not allow abortion
This school allows the use of computers during exams
3: With a noun phrase patient/object and an infinitive complement (what they're being allowed to do):
He won't allow me to leave
Some states allow automatic weapons to be kept at home
It is worth noting that last example, showing that the "patient" direct object (who/what is being allowed to do something) doesn't need to be a person (in this case, it's automatic weapons).
It's also worth noting that you may see things like "The iPad allows to surf the Internet on the move", with no "patient" object. These are not considered grammatical (they're usually from non-native speakers).
(In case it is not obvious from the above, OP's #1 is ungrammatical. All the others are fine.)
I cannot find any specific questions about the closely-related verb let on either ELL or ELU, but I'll just make one final point here. Be aware that syntactically, let doesn't work exactly the same as allow.
Definition of "allow for" from Wiktionary:
To take into account when making plans.
The problem is that they didn't allow for the extra centimetre of overlap. So it didn't fit correctly.
The whole time is 60 minutes. If it was 45, it would say
The talk needs to be approximately 45 mins including 15 mins of Q&A’s.
It would help to know the context, but that sentence strongly implies that whoever is giving the talk has been allotted 60 minutes, so the talk needs to be limited to 45 minutes so that there are still at least 15 minutes left for Q&A.
In other words, since you only have 60 minutes, you must limit the talk to allow for Q&A time.
Best Answer
Allow and allow of have essentially the same meaning, “permit”. They differ in the sorts of complements they license.
Allow licenses nominal phrases, gerund clauses (with optional possessive subjects), and infinitive clauses with objective subjects:
Allow of licenses nominal phrases and gerund clauses, but not infinitive clauses:
Allow of has never been common, and it has practically disappeared today: —Google NGrams
Allow for has a different meaning: it means to ‘take into account’ or ‘make provision for’. For instance, we might say:
We would not say that the evidence allows for a possibility, because evidence is not a viable subject for that action; it is rather your interpretation which must allow for possibilities:
Note, however, that these terms are so similar that they allow of easy confusion, so in your reading you must allow for the possibility that the writers have misused whichever terms they use.