You can specify a range of dates when your observations should be executed in the ALMA Observing Tool. Proposals may involve time-critical, multiple-epoch observations, and continuous monitoring of a target over a fixed time interval, but their execution is restricted to the time slots reserved for science observations.

Therefore observations of monitoring and time-constrained projects are offered subject to the following restrictions:
• Observations to be performed with two 12-m Array configurations to satisfy the PI requests of AR and LAS within a SG are not allowed to have time constraints.
• Observations with one 12-m Array configuration and the ACA are allowed to have time constraints only if simultaneous observations with the two arrays have been requested.
• No restrictions will be imposed on the size of the time window specified by PIs for time-critical observations. The scheduling feasibility of any proposal will depend on the total number of constraints that are imposed and on whether the time window takes place during other activities on the array such as engineering or computing time. Whether such observations are technically feasible will be decided on a case-by-case basis. In particular, observations with strict timing constraints but many possible time windows may be feasible.
• Programs that require more than two hours of continuous observations to monitor a source cannot be guaranteed due to variable weather conditions and system interruptions. Proposer may request monitoring observations longer than two hours, but if the observations fail after two hours, the observations will not be repeated. Monitoring observations will be interrupted by regular calibrations.

Stand-alone ACA proposals requesting only observations on the 7-m Array are allowed to have time constraints.

This should not prevent observations of recurring phenomena with predictable times (such as, say, maximum elongations of planetary satellites), as long as their occurrences are spread over a sufficiently wide fraction of the observing period in a cycle and as long as the number of epochs that need to be observed remains relatively small with respect to the total number of suitable epochs across the cycle.

Please refer to Appendix section "Time-Constrained Observations" of the ALMA Proposer's Guide for more information on time-critical and monitoring observation.

You can read how to include time constraints in Section "Time-constrained observing" of the Observing Tool User Manual.