After reading the paper I believe they do both aspects that you mention: i) they give XGboost and all the baselines up to 4 CPU days of hyperparameter optimization time on 20 CPU core servers per dataset, same compute as the author's proposed method. ii) the search space for the XGBoost hyperparameters includes low eta (starting from 0.001) and large num_round ranges (up to 1000 trees) in Table 5 at the appendix.