documentation already answers your question:
Each query sent to the Google Maps Distance Matrix API is limited by the number of allowed elements, where the number of destinations defines the number of elements.
Below we have the API limits:
Users of the standard API:
- 2,500 free elements per day
- Maximum of 25 origins or 25 destinations per request
- 100 elements per query
- 100 elements per 10 seconds
That is, if per day you can search for 2500 elements and each query can have up to 100 elements, you can do at least 25 queries per day.
It is also worth noting that each request can have a maximum of 25 origins or 25 destinations, so in that case they would be limited to 4 destinations or 4 origins respectively. (25 * 4 = 100)