There is not such an option to limit number of subchannels in pick first, currently.
Using a custom resolver as sanjaypujare@ mentioned might be an option. I will note though, the c-core resolver API is not a public API nor is it stable.
The best option here probably depends on how these connect attempts are failing i.e. why each connect attempt is taking so long that the sum is a problem.
A few things I can think of:
a) Can you limit the number of addresses in DNS records?
c) If a certain set of address consistently fails to connect (e.g. IPv6 addresses or IPv4 addresses), can you, for example, configure routing tables in order to make connect attempts to those addresses fail fast?