We study how the learning of argument structure constructions in a second language (L2) is affected by two basic input properties often discussed in literature – the amount of input and the time of L2 onset. To isolate the impact of the two factors on learning, we use a computational model that simulates bilingual construction learning. In the first two experiments we manipulate the sheer amount of L2 exposure, both in absolute and in relative terms (that is, in relation to the amount of L1 exposure). The results show that higher cumulative amount of L2 exposure leads to higher performance. In the third experiment we manipulate the prior amount of L1 input before the L2 onset (that is, the time of L2 onset). Given equal exposure, we find no negative effect of the later onset on learners’ performance. This has implications for theories of order of acquisition and bilingual construction learning.