How do I know what my end clients invoicing cycle and payment terms are? Do you think I could negotiate with them on them?

This should be listed in the agreement you have with them

If your client has a master or Terms of Business the invoicing cycle and payment terms are listed. In some instances, this can be negotiated with them or the question asked. Please note extended payment terms, where the invoicing cycle and payment terms exceed 30 days an extended payment term of 1.00% may be changed, please consider this in any invoicing and payment term negotiations.